C# For Absolute Beginners with Game Design

1. 0-1. Is This The Course For You and About The Instructor: So welcome everybody. Welcome to my C Sharp video tutorial course. Here I have around 11 hours of footage teaching you everything from the absolute basics. This assumes you have zero programming knowledge at all. And at the end of this, you will have the same, if not more, knowledge, about programming and C Sharp than a typical university graduate student. So if you want to learn C sharp as a hobby, it's no problem. You're going to get that out of this course. However, if you want to get a job or potentially a career at the back of this course, then again you're going to have no problem doing that either. And for those of you that perhaps want a C Sharp refresher or a generic programming refresher, then this course is also good for that as well. So is this shop video tutorial course good for you? Well, do you want to learn shop? Then the answer is yes. But perhaps a better question is why should I choose this course over any others? Well, the secret to learning is, number one, the teacher, and it's how the teacher teaches the information. And number two, the learning process. Is the course engaging? Yes, it is. Is it boring? No, certainly not. Is it confusing? No, because I explain principles in not just one way, but perhaps two or three different ways. So at the end of this, you're going to get a full understanding of every technique that I teach you in this course. And the pacing, is it fast pacing? No, it is not fast pacing at all. This course is designed for absolute beginners. So the pacing is slow, at best. Who is this course for? This course is for absolute beginners. It assumes you have zero programming knowledge, zero software development knowledge, and you want to get started with C sharp programming. Maybe you want to do some games in Unity. Maybe you want to develop software applications, mobile apps, websites in C shop. All of that is achievable by watching this video tutorial course. This course does assume you know how to use a computer. You know generically, you can move a mouse, maybe check your e mails, and download a file. But the point is, it doesn't assume any programming knowledge at all. So the learning experience, well, I enjoy psychology in my free time, so I understand how the human mind works, especially when learning and retaining information. But perhaps a new and daunting subject. So that brings me to the next point, the pacing. What is the pacing of the course like? Well, programming has a lot of big and complicated technical words. But don't worry, I introduce technical words very slowly throughout the course. Many teachers use complicated words immediately, and it causes a lot of confusion and it hampers the ability to retain the topic at hand. I find this a very important step to prevent your biggest enemy, which is information overload. So don't worry, you're going to learn the complicated and technical words, but not before the topic at hand. I will introduce it slowly so that the learning experience is a very enjoyable one. So as the course progresses, I'll slowly start introducing the correct industry terms and technical jargon when watching the videos from this course. I appreciate you're not there to ask questions immediately and get direct feedback. So what I do, I explain topics in various different ways, not just one way, and that way you can fully understand the subject at hand. I feel this method of learning is far better than making videos where you don't provide enough information. If not enough information is provided, then you feel lost and frustrated and there's no teacher there to ask any questions. You will not experience this with my course. And I guarantee that because even after I've explained a complicated subject, for example, in numerous different ways, then if you have any questions, you can feel free to leave me a message or a comment. And I'll be more than happy to address any questions or concerns you have at any moment during this course. And lastly, if I teach you a programming principle, I don't just teach you the information. I actually explain why they're useful, why you apply this in everyday life, and why it's important in C sharp development to do this particular principle. So that is where my course differs from a lot of courses out there. You learn the how and the what, but also the why, which is very important. Engagement, one of the biggest killers of learning new information is engagement and motivation. The two kind go hand in hand. So what I do, I use fun examples. Also, I use trending examples as well to keep things interesting. I understand what it feels like to lose motivation and lose engagement and get a bit bored when learning a new topic. So I try to keep things fresh and current so that you'll never lose motivation. And you'll always stay engaged with the topics at hand. So what will I get out of learning this course? Why should I learn from you? What is the end result? What can I achieve? Well, very good questions. I will teach you everything you need to know about shop, but not only C shop programming in general. The tools and techniques and principles to make you a good developer, a good programmer, especially in shop. And it's going to be similar, if not better, than a university graduate student. How do I guarantee these bold claims? Well, I've been to university, I went for four whole years. And I can guarantee that the content of this course is exactly what I learned in university. But not only that, but more. And I also teach you the tools, techniques, and best practices that I've picked up working in industry as well, so in a professional capacity. So whether you go to university college or you don't go, you have an advantage because you're not sitting in a classroom full of people with a lot of distractions. This is a unique one on one experience. So lastly, I'll summarize by saying, it doesn't matter what type of learner you are, whether you're a visual learner or not a visual learner, you can watch this course by sitting in a chair and eating a pizza, for example. However, if you want to be more interactive, then I provide the full project files along with this course, all the source code that I use. So if you want to follow along at your computer, you can do that. No problems at all. This course offers multiple ways of learning for various different types of learners out there. So about me, who am I, What is my name? Well, I'm Sean and it's nice to meet you all. I'm a professional, self employed software engineer. But not only that, but I teach software development and programming. I work with many different programming languages and also many different architectures. But because I regularly teach students, I haven't lost the ability to communicate with new learners, especially on a beginner level. I graduated university now back in 2007. I have over 20 years of professional experience in software development. I was even working alongside my university studies in the same field. I've been teaching programming now since 2003. So a long time ago, I used it as a way to fund my university studies before Youtube was even a thing. I'll show you my very old website now where I made video tutorial courses in Visual Basic, six C plus plus Java, Direct X, and various things. So you can see that now I've taught many people programming. And they always come back to me later, you know, ten years later, 15 years later. And tell me all about their success stories, the companies they're working at now, and what projects they've been involved in. So it's really wholesome and interesting to hear these success stories from my past students. And I love it when students come back to me and tell me about their success stories and how their life has changed. Learning, programming, it's really interesting and it's the best part about teaching. So I'm self employed now, but I've worked for many businesses in the past. Small companies and large ones too, perhaps you've heard of a few. I've worked for The Guardian, which is a newspaper company based out of central London. I've worked for the British Ministry of Defense, where we worked on Cad software for modeling their surface ships and submarines. I've worked for Pfizer, a pharmaceutical company, which I'm sure you've all heard about these days. But when I was working there, not many people have heard of that company. And I've worked for various small agencies that perhaps I'm sure you've never heard of. So I can share my experiences from working in small teams and also very large teams. And examples of both of these different types of experiences I'll share throughout this course as well. So if you are wondering where my accent is from, Well, I was born in the UK and my programming ventures have taken me all around the world. I moved to America when I was 25 and got citizenship there. And now I'm living in South America. But one thing that has remained consistent, rather than my home and my accent, for example, is that I've always been teaching programming and I've always been doing software development. So enough about me. Let's talk about C sharp now. 2. 0-2. What is C# in Game Design? and Why Learn C#?: So what is C Sharp? Well, C sharp is what's called an object oriented programming language. And don't worry, we'll be talking all about that later. It's created by Microsoft and it runs on what's called the.net Framework. C Sharp has its roots in the C family. So I don't know if you've heard of C or C Plus Plus, but it's quite similar to those languages, and this is where it was developed from. It's very similar to popular languages like C plus Plus and Java. And the first version of C Sharp was released in the year 2002. Now, so it's over 20 years old. And the latest version at time of filming is C Sharp version 11. So the C Sharp language slowly evolves pretty much like everything else in life. So why should I learn C Sharp? What is it used for? Well, you can create mobile applications, desktop applications, web applications like websites, video games, virtual reality games, for example, machine learning, software, database applications, and much, much more. It's one of the most popular programming languages in the world. And this is why it's really good to learn a language like C Sharp because there will be more job opportunities out there and more opportunities for you to apply your knowledge. It's easy to learn and it's simple to use. It has huge community support. If you already know C or C plus plus or Java, or maybe you want to learn them in the future, then they're very similar. The principles I teach you in this course, you can apply to C plus plus and Java if you wish to pick up a new language in the future. One of the trending things right now is to create video games in a software development package called Unity. Unity supports C Sharp behind the scenes. If you want to make your video game do things, make your characters move, then you can use C sharp to accomplish this. So right now, people are learning C sharp more than ever, just so they can create video games in Unity. So here is a lot of reasons to learn C sharp and why you should learn C Sharp over perhaps other languages. So hopefully, through my explanation so far, I've convinced you to begin your journey in learning C Sharp and becoming perhaps a professional, or even a hobbyist, programmer. Now let's begin our adventures in C Sharp and download the tools we need in order to get started. 3. 0-3. Downloading and Installing Visual Studio (C# IDE): How do we start coding in C Sharp? Well, the easiest way to get started is to use what's called an IDE. This stands for Integrated Development Environment. And the environment we're going to be using is called Visual Studio. So we're not going to be coding in Notepad or anything scary like that. We're going to be using beginner, user friendly tools which are provided by Microsoft. And not only that, they're free of charge. Let me show you how to download and get started with Visual Studio. Let's start downloading Visual Studio now. If we come over to Google and just type in Visual Studio Community, and we can click the first result right here. Now, the latest version at the moment at time of filming is Visual Studio 2022. But even if you have an earlier version or a later version, a lot of the techniques we're going to be covering in this course are going to work. No problems. So we're going to click this first link here. Here we can download the IDE right here if you're using an Apple Mac, for example. Then you can click this button up here. And then Visual Studio comes in three various flavors. We have the one for Windows right here, the one for the Macos, and also a lightweight one for Mac, Windows, and Linux. So depending on your operating system, you should be pretty much covered. But I'm running a Windows machine and that doesn't really match. If you run Mac, you can still follow the tutorials, no problem. So I'm going to click this download link here, and then Visual Studio is going to start downloading. It's only a 34 megabyte file, so it's very small, But everything will be downloaded inside the set up file itself. Just before we install Visual Studio, I want to mention one thing. Visual Studio is not just tied to C Sharp development. You can do so much in visual studio. Visual studio works with HTML, CSS, Javascript. You can even create mobile applications, Php, Python, Spot, Net. All these various things, tools, technologies, and programming languages you can do in visual studio. So if you already know a different language, or maybe you want to try different languages in the future after looking at C Sharp, then Visual Studio will support you through those endeavors as well. So it's a very powerful piece of software, and again, it's free. Let's open the Visual Studio setup file, which we just downloaded and get with installing Visual Studio. So let's click continue here. Now it's just preparing the installer, it's downloading a slightly bigger file. Now this is the window that you're going to see once the set up is initialized. So lots of different things you can do here for the purposes of this course. The only thing we're going to be working with is C Sharp. The only thing we need is the.net Desktop Environment right here. So you just click this box right here, and then we can get with installing these components. Anything else? Here is totally optional, and up to you, we have various things for developing websites in Aspet. We also have Azure Node, Python. Again, desktop and mobile stuff, stuff in C Plus Plus. And you can even install Unity from inside the visual studio installer and various data components as well. So there's lots to be done, lots to install, and lots to learn in terms of programming and working with visual studio. But for what we need is only this simple box right here. If you speak another language or you're more familiar with a different language, you can select it from here. It's no problem at all. So if we come over to here now, this is everything that's going to be installed here. To be honest, I don't think we need live share model builders or blend. It's just going to blow our installation. But I think this is a good set up to get started with and it's going to give you everything you need to follow this course and even slightly more. So now what we're going to do is just click this install button. Here you have a couple of options. You can download it all, then install, or you can install while downloading. It doesn't really matter, it just depends on your preference and perhaps your Internet connection. So let's click the install button and get started. The installation may take a few minutes, but once you see this screen right here, that means visual studio has been successfully installed. You may also have icons on your desktop or in your programs menu, depending what operating system you're running. But essentially, once it appears in this list, then you have Visual Studio installed. What we can do, we can just click this button now and launch Visual Studio, and then get started with our software development in C. Sharp. 4. 1-1. Hello World (Mr. Beast Logo): In this lesson, we're going to create a very simple piece of software called a console application, and it's going to display the Mr. Beast logo to whoever opens our piece of software. Let's get going now. Visual Studio has been freshly installed. We're going to create our very first software application. It's going to be our very first one. It's going to be beginner friendly, and we're going to take it from the top. Let's get going. Once Visual Studio is open, we're going to click File, New Project. Then we'll have a window that looks similar to this. Now if you don't have Visual Studio 2022, that's the version I'm using right now. It may look slightly different. You may see settings in different places. Things might be called something slightly different. But the general kind of principle still applies. Now our very first software application, it's going to be a console app. And this is represented by this project template here. What a console application is, it's kind of like a black window. It just has text on it. And the reason I'm using that is because it's very beginner friendly. There's no buttons, lists, images, or anything complicated. This is very beginner friendly and this is why I'm using a console application. If you don't actually see that in this list, you can search for it here by typing in console app or console application. And you can see all these templates will load up here. We want this one because we're writing in C Sharp. It actually will run on Linux, Mac, Windows. We're going to use this one, we're going to click next. We can call this whatever we want. It's up to you. You can leave it like that, or you can choose something more descriptive. So we're going to call it first program, the location. You can choose a directory where you want to keep all your project files. That is up to you. So let's click next. Now this framework, I'm going to talk of all about frameworks in a later tutorial. I want to keep this very simple, this list, it might have 4567, all different numbers. We're just going to leave it at seven. If your four is fine, it's still going to work. If you see this checkbox here that says, do not use top level statements. Make sure it's checked. This is very important. Let's click Create. And this is what we see right here. Now Visual Studio is actually given all of this code for us, and the reason they do that is to make it more user friendly so we can get started. As a first time user, you probably have no idea what this means. That doesn't really matter. All of these lines here I'll be covering in a later tutorial and you will learn what they mean in time to keep this beginner friendly. The only line right now anyway, you need to concern yourself with is this one right here in this tutorial. We're going to put all our code between this curly brace here and this one here, all in the middle. And we can put more lines in here if we want to. In this tutorial, we're only talking about this section here. Do not worry about any of this. Let's remove all that complexity. Let's talk about this. What does it do? It says console right line, Hello world. In order to actually try and run this program, I need to talk about what is called a compiler. Now, Visual Studio, it has an inbuilt compiler because we're writing C Sharp. It has a Sharp compiler in there. What the C Sharp compiler does, it takes all our code here, that's everything in this white window, compiles it. If we're using Windows, for example, it's going to create an EX file for us what an E file is. It's called a binary file, maybe you don't really need to know that right now, but it's called a binary file. If we want to run this program on say, a Mac, for example, then it's going to create a binary file that a Mac would understand. If we want it to run an Android, like an Android phone, it will create a binary file that the Android phone can understand. That's really what a compiler does in a very small, non complicated nutshell. It takes all of our code and compiles it into one binary file. In order to do that, in order to run the compiler, you see this little green play button up here where it says our project name called First Program. When we click this button, this is where we say, oh, hey, Visual Studio. Can you tell our compiler to take all our code and make it into a file so we can run the software? That is exactly what it does, so we're going to click this right here. What happens is our little black window appears and immediately disappears. Two things here, all of this stuff down here, you saw all that text going crazy. That is the compiler. The compiler is saying, okay, I've done this, this, this, can I spat out this EXE file at the bottom of it? That's because I'm using Windows. It's created an EXE file for me. Now the EXC file has been created. The software is run. It tries to open the EC file for us. That was that black window that just appeared. But then it instantly disappeared. It instantly disappeared because we're not actually telling it to stay open. Visual Studio did a good job of putting in this sample code for us, but it also keep the software open so we can actually see what is going on. I'm going to type one more line and that's going to keep the black window open for us. So I'm going to type console because console is the black window. So we want to say, oh, hey, console read line, right? So that is what I'm putting there and that will keep the console window open. Let's talk about this line real quick. What this does, it waits for user input. So for example, have you seen a software, any piece of software that says, hey, what is your name? And then you type your name? So what happens is when we run this line of code, the black window is waiting for our input. And that just keeps the window open. Let's just run this software now. Now you can see the window is open. It's actually stayed open, It's not going away. That's just because it's waiting for our user input. But it's kind of like a little dirty, kind of hacky way of keeping. So we can see what is going on. This black window here is our console application. It's our very first piece of software. Pat yourselves on the pack. It doesn't do much. The only thing it does is say hello world. It's telling you it's alive. It's saying hello to the world. That's all it does right now. Very simple, but don't sell yourself short, it's your very first piece of software. We can either close this by hitting Enter or crossing it off here. And that is it in our nutshell, our very first software application. Now how do we expand on this? Well, let's talk about one other thing first, that is case sensitivity in C sharp. And a few little caveats as well. You notice here where it says red line and right line, it's actually case sensitive. What that means is if I change this upper case L to a lower case L, you can see I have this red line underneath that's saying, oh, I can't actually find this in the system. It doesn't exist. That's because a lower case L and an upper case L in C sharp are two very different things. Bear that in mind. It needs to be case sensitive. The last thing is that all lines must end with a semi colon. If you forget the semi colon, then we're going to get a similar thing happen. You see this little red squiggle here. If we hover over that with the mouse, it's saying semicolon expected. So it's actually telling you what the problem is. If you ever have an era where you have the red squiggly line and you try and run the program, you're going to get something like this. And you will get very familiar with this dialogue in your programming ventures, trust me. And then it'll tell you what the problem is down here. You can double click it and it alerts you to this. And that's just saying the semicolon is missing. Now, I've talked very briefly about what these do. Let's just talk about this bit here. What we want to do is say, oh, hey, black window. Write the line to the window and we want to write hello world. That is all it's doing. You fully worked that out yourself. But now I've told you that we can actually expand on this. We can actually say, oh, hey, that's right, Three hello worlds. We save that, click the button, and now we have three of those. Now you see where this is going in our example. Right at the start I said we're going to display the Mr. Beast logo. Now I have an ask file for the Mr. Beast logo. Ski is just a text representation of an image. I'll show you what that means now. It's all going to make sense. So you can see here, I have a Mr. Beast logo here in Notepad. And I've added the console right lines before it, so we can see that here. I'm just going to copy all of that. And I'm going to paste it between these curly braces like I talked about earlier right there. I'm going to save that. I'm going to press the green button. I'm going to open this window so we can see it. And I'm going to scroll up. That's our very first piece of software. As soon as someone opens your piece of software, they're going to see the Mr. Beast logo. It's that simple how we can modify that message and create a whole new picture. When we look into the code here, it's just multiple right line statements that creates all these Ms here and a very nice character design on the logo here. Before I end this lesson, I'm just going to show you how this all ties together. It makes sense in your head. Remember when we created a brand new project and we have this location field? Well, I'm just going to go into this folder right now. Now I'm in that directory on our computer. We can see Visual Studios created a series of folders and files for us. Inside here we have what's called a solution file here, and it's created another folder. So we'll go in there. It's created even more files. This one has our coding. But if we look inside this bin folder here, and then inside this debug folder right here, inside this one, you can see there's a few files right here in the middle here. This is our binary file, and because I'm using Windows, it's created an EXE file, Fas. If we double click this, we can even send it to a friend, for example. They can double click it. When you maximize it, you can see the Mr. Beast logo. You can see this is how it all ties together. Visual Studio tells the compiler, oh hey, take all the code, Create a EXE file, Fas, and put it in this folder right here. All of the other files I'll talk about at a later date. But for the purpose of simplicity, it creates our EXE file fas, and that is our very first piece of software. 5. 1-2. Variables: Now we're going to talk about is I'm going to introduce a very simple variable. I'm going to show you how it works, what variables are and how they can benefit and things like that, variables. Let's talk about what they are. For a start, we have a sample application here. It just says, hello world to a black window. And that's all it does, as you can see right there. Now I'm going to introduce what's called a variable and I'm going to talk about how they can help us. Let's just introduce a variable. I can talk about this in a second. I'm going to call it test. We're going to give it a value of Hello world. I'm just going to put the variable name here. So let's talk about this and what this does. So what I'm doing here, I'm initializing what's called a variable. Now this is the variable. It's called test, so this is the name of our variable. Now this variable can be called anything you want. It could be called ham sandwich. It really doesn't matter. But the point is you need to give it a name where it makes sense to you, you can refer to it. Because when you have a software application that has thousands of variables, you're going to get very confused if you call them all different types of sandwiches or random names like test or something like that. So it needs to make sense to you. So I'm just going to call it hello World. So that's the name of our variable, this is the value of our variable. So this is what we're putting inside our variable here. Now this part here is what's called a type. Now this is a string variable. What a string variable is, it's a container for words, sentences. You can put a whole book in here if you would like. It's all alphanumeric letters and numbers, but as a string, it's not numbers by themselves, it's not a decimal value, it's not a date or a time or anything complicated like that. That's what a string is. That's what's called a variable type. That's the variable type that's saying, hey, computer, we want to start a new variable and put it into memory. The name of our variable is this. The equal sign is how we initialize it, like give it a value. When you're working with strings, we always put the value in double quotes. Like inside the double quotes is the value for our variable. We always end every line with a semi colon. Now our variable is called Hello World. Let's run the program. You can see it outputs Hello World to the window. It does exactly the same as it did before. That's to be expected because we haven't changed anything. We've just declared and initialized a variable and we're outputting it to the black window like before. Exactly the same thing we're doing here. One thing real quick, with variable names, what I always do is use title case always with a lower character at the start. Now this is up to you, but generally this is how people tend to use variables. Maybe when you work in a company in the future, if that's what you want to do, other people will do a similar thing. It's good to introduce good practices. Now, that's the only reason I do that. Then every next word, hello world. This will have upper case. If we have another word here, then that one will start with upper case. That's just what's called standards, it's optional. Let's talk about what declaration is and what initialization is to cover those two terms. I'm going to expand on our little example here. I'm now going to how are you like that? And then I'm going to re output the variable to the screen. Then I'm going to run the application. So you can see what is going on. You can see here in the window it says, hello world. How are you? Have a look at how that works? You can see here, we've defined our variable, we've given it a type. Now, we only give the variable a type once. We're saying, oh, hey, computer, this is our variable I want to use. This is our new variable, by the way, it's a string variable. Now, we've done that one time. We no longer need to tell the computer it's a string, the computer already knows and it remembers this. Now, every time we modify our variable, give it a new value, we're just going to overwrite what is already in there. When this line comes along, this part will be replaced with how are you? And then we're putting it back out here. We don't have to declare and initialize our variable on one line. Let's take a look at this example here. I could equally do this. The same thing will happen. What I'm doing here, I'm declaring our variable, declaring means hey, computer, I want to create a new variable. I know it's going to be a string, but I don't know what the value is going to be yet. Maybe I'll decide at a later time. At a later time. Okay, I've decided what the value will be. It's going to be hello World. Then I want to output it to the screen. And then I'm re initializing it here and outputting it to the screen. This is declaration or declaring a variable. This is initialization or assignment. There's some words you're going to hear in the future if you continue to program with C Sharp. You can see we're doing this on two lines and the output is exactly the same as before, which is to be expected. One last thing, If we declare a variable here and we attempt to output it without initializing it or assigning it, then it's going to throw an error. We can see this red squigly line. When we hover our mouse over the red line, we have a little bit of a clue as to what the problem is. And it's just saying use of unassigned variable, hello world. It's telling us what the problem is. Anytime we have an error, we can't run the program because we always need to fix these errors. That is a very basic view on how variables work in C sharp. 6. 1-3. Data Types: Okay, let's talk about data types, what they are, how they can help us, why we can use them, and everything in between. So I have a sample application here. It doesn't really do much. We declare and initialize two string variables here, and we output them to our black window. When I run the application here, it just says Sponge Bob square pants. I thought of an example on how to explain data types a lot easier. I came up with an example. Have you ever played Top Trumps or Pokemon cards or gear or something like that, where you have the name of the character, maybe some attributes like age, weight, height, rarity, or things like that. I think that would represent data types quite well. And help me explain them so you understand them a lot easier. Imagine a card that has a name and it might have an age. For example, this is the age of the character. Now Sponge Bob is one of those characters that transcends all age. I'm going to put 21. This is a string type variable, This is a data type. Another data type we can use is what's called an integer. Now what an integer is, it's a number. We can actually hover over it and visual studio actually gives us more information about this. It represents a 32 bit signed integer 32 bit just means the size. How much information you can put in here. I think it's anywhere from negative 2 billion to positive 2 billion. I think using age fits this quite well, it's only going to be 23 digits. When we use integer type variables, we don't need these double quotes like on strings. We just need a number right here. Another one, maybe the weight, and that will be in pounds. Maybe this sponge is around 120 pounds, something like that. Another one height. Now height, we're going to put it in feet and inches. I'm going to put it in feet and inches so I can show you a new data type. This is called a double. Now what a double is, it represents decimal numbers. Let's put height in here. Let's say our sponge is three feet, 4 ", for example. Something like that. So that's the height of our sponge. If we have a over double here, it represents a double precision floating point. Very complicated, isn't it? And this is why people learn from tutorials, a double represents a decimal. This is anything with a decimal point. Now, decimals. Let's talk about decimals real quick. In C sharp, we can represent a decimal number in one of three ways. Another one is called a float. Let's put numbers after this. When you use a variable, they all need to have unique names. Let's do decimal. That's another way how we can decimal numbers. These are the three ways we can represent decimals in C sharp. The main difference is the precision. Now float is, I believe, 32 bit. It's only seven digits. You can give it more than seven digits, but it will cut it off. Truncate it at seven. You lose everything after seven digits, which is all this accuracy here. Now a 64 bit. Slightly more, I believe. 15 digits, 15 to 16 digits. So it's more accurate. So we can put up to 15 in here. By default, a double is used when you use decimal numbers in C sharp. When I say default, I'll explain that in a second. The last one is decimal. This one is, I think it's 128 bit, lots and lots of digits. I think 28 digits, quite long. We use decimals when we talk about things to do with money. Maybe if you write an application to handle taxes as a government agency, for example, we want to make sure everyone pays their taxes to really far out their decimal point. When you deal with money, it needs to be really, really accurate and that's where we would use a decimal. You can see here when I initialize this float data type variable height one, I put a little F at the end here. This tell C sharp. Hey, I want to initialize a float value. This is because it uses double as default. You can see when I initialize a double, I don't need to put a letter at the end. Anytime I put a decimal value here, C sharp will assume it's a double. If I want to initialize a float here, I have to say, oh, by the way, this is a float data type. Because if I don't do that, you can see there's a red line. I hover over it. It says, literal type double cannot be implicitly complicated, isn't it? It basically says, use an suffix to create a literal of this type. It's basically saying, hey, you have a float data type, put an F at the end and then we're happy. Same with decimal, I don't know whither you don't use a D or something more descriptive, it's probably used by something else. This one wants an M. And similarly, if we don't put an M, it's telling you to put an M. This is why IDEs is called IDE, like visual studio, really good. It's actually telling you what you're missing and what you need to do. If you use something like Notepad, it's not going to tell you this. It helps you program a lot faster. So these are the three ways we can represent decimal numbers and we're just going to use a double for the height. The height of our sponge is three point, I don't know, three feet, 4 ", something like that. I think that would be good. Now, the next one I want to introduce is a Bolen represented by bool. This what could the booling be? Whether our trading card is first addition? So I'm going to put is first addition. I'm going to say true. Spongebob is a very rare trading card and it's first addition, so it's going to be true. Now booling data types can have the value true or they can have the value false. Only one of those two values true. If it's yes or false. No. That's how we use boolings in C sharp. It's true or false. Only two valuables. If you want a variable that might have three or four values, then don't use a booling. Booling are for only two values. The last one I'm going to talk about now, there's loads of data types in C Sharp, We can do dates, times, various complicated things like lists and things like that. But to be honest with strings, integers, decimal values like the double boolings and characters, here we can pretty much write anything, lots and lots of software with only these data types. Perhaps we will cover more in the future. The last one I'm going to talk about is characters represented by Shah, right here. For this, I'm going to call it grade. The grade of our card, is it excellent? So that might be a or is it bad? That could be an. Then an average card might be like when you take an exam. So our grade might be something like that. And this is a very good card. It's first edition mint quality give it a grade of A. When you initialize character variables, we use single quotes, not double quotes here. Visual studio does a good job here. If you forget the quotes, it will probably tell you you need them or give you a cryptic error like this one. Yeah, so now we've declared and initialized all our various variables with all their different types. Now I just want to output them to the screen. You can see they have the green line under each one right now when I use age down here. Watch that green line disappear under age, and that's because we're now using it now. I'm going to put one for every different variable here through the power of editing. We can see here now we're outputting all of these to the screen if we run this application. Now we can see all our various values for all our different variables. We see the first name, the last name, the age, the weight, the height. True because it's first edition and also it's a very good trading card. 7. 1-4. C# - A Strongly Statically Typed Language: I want to talk about two things now to do with C Sharp, now that we understand what data types are. Now C Sharp is what's called a strongly typed language and also a statically typed language. Let's talk about what those two terms are. A strongly typed language, that means once we've defined a variable called first name and we've given it the data type string, it has to be a string throughout its whole lifetime of the application. We cannot, for example, take first name and then give it an integer value because it won't like that. That's because it's a strongly typed language. However, if you use a language like Python, for example, you can do this, it's no problem at all. That's because it's not a strongly typed language. In this case, that's what a strongly typed language is. Once you've defined a string, you've given it a unique name. You cannot then stuff a different data type into here. You can't say, oh, now I want to say it's true, For example, it's not going to work. It's going to tell you that's what strongly typed language such as C Sharp, the last one is what's called a statically typed language. If we make an error to do with one of these data types, for example, we have first name. Therefore it expects a string in double quotes, like here, if we give it an integer, it's going to complain. It's going to give a red line underneath when. Anytime we have a red line underneath, something like this error here, we can't compile the application. It's not going to letters, it's not going to letters. For example, if you're using Windows, compile your code into an EXC file and give it to a friend to run. It's not going to work. That's because these errors are caught at compile time. And that's what a statically typed language is. If we make an error such as this, we're not going to discover it at a later date when a user is using the software. That's quite a good advantage of C Sharp and also languages like C plus plus, very similar. Once we have a data type string, it needs a string value. These errors will be caught at compile time. And that's when we press this green little Play button here. That's what a strongly typed language is. And also a statically typed language, C Sharp is both of these. 8. 1-5. Working with Strings and Substrings: Okay, let's look at how we can work with some string type variables in C sharp. Here we have a sample application. We just have first name, last name, and we're outputting both of those two our console window. Now, how can we actually join two strings together? I have one variable first name, one variable last name. Right now it puts them separately on two different lines. But how do I join these together? What we can do here, what's called concatenating two strings, and that's just a fancy way of saying join them together. Concatenation, it could be like concat for short. These are words you're going to hear perhaps in the future if you continue your C sharp journey. Let's look at joining these two strings together. What I'm going to do, I'm going to use what's called a operator. So you can see this plus here. And what that does, it just takes this, this string and joins them together. Very simple, isn't it? So now we run the application. We can see we have sponge Bob, square pants on one line. But you can see there's no white space in between here. So let's look at adding that. What we can do here is add another string and use the plus symbol. Again, what we're doing here, we're taking the first variable, first name. We're concatenating it, joining it to this empty y space, which is also a string. And then joining it to the last name, which is a variable here. Now, this isn't a variable, we don't need variables in here. We could easily do this, and it's exactly the same. That way we're not even using that variable, but the output will be exactly the same. That's how we can join two strings together. Just so you fully understand, we can even create a variable here and we can do first name plus last name. Then we can put full name in here and we're going to have exactly the same result. Let's not forget our white space here. It looks presentable and we're going to run the application. You can see here we have exactly the same result. We're just using a variable here called full name. And that's just adding these together, concatinating them together, white space. That's how we can join two strings together, Very simply, substrings. What is a substring? Now, a substring is just one of many different things you can do with strings in C sharp. Here's an example. Here we have a variable called name. It has sponge Bob square pound sets the value. And we're out putting it to the screen now, for example, say I want to extract a certain part of this string. I want to extract the word sponge from it. I don't want the rest of this stuff, I only want this part right here. Now what we can do, we can use something called a substring method to extract a portion of our string. And that's what a substring is. It's a part of a string. I could take this, I could take this. I could take anything I want. I could even take one letter if I wanted. Let's look at how we can actually use a substring. What I'm going to do, I want to extract sponge, the variable. We can call it what we want, let's call it sponge. Why not? We want to initialize sponge so we use our equal sign. When we work with a variable, what we can do is put the name of the variable here, which is name, in this case when we use a period or a dart, whatever you want to call it. Afterwards we have all these different things we can do with it. Some of the common ones are always at the top with this black star next to them. One of them is substring. We can do lots of things we can replace. We can lower the characters. We can split it, lots of different things we can do. Substring is what we want to use. We can double click this when we open parentheses here, we have a few options we can do with it. Now, I'm going to talk about this stuff a lot later when I talk about methods. But for the most part, I'm just going to put two things in here. And that is what I want to do here. Now, in C sharp, everything starts at zero. Index is at zero. This string here, this character here, that is position zero. The P is position 123. Everything starts at zero. Remember that moving forward is character position zero of our string sponge Bob square pants. So the first value here is zero because we want to start at position zero. Then the next value is how many letters you want to extract from the string sponge 12345. It's actually six. Now we want to extract the first six characters sponge right here. These are the values we put in here. Now if this is confusing to you, let's go back to where we talked about console right line. We had console right line and we opened the parentheses in here. We want to put our variable onto the black window. Now substring, in this example, we want to give it two values. And when we give it two values, we separate them with a comma like so we want the first character and we want to count six characters forward which we should extract sponge. Now we want to put sponge on our console window so we can actually see the result. Let's compile our application. We can see with output sponge right here. That is very simplistically how the substring works. If we want to extract, say, Bob for example, then we start a position six and count three characters forward. Then we can see we've extracted Bob, That is how a substring works. One other thing we can do is what's called a replacement. We have sponge Bob square pants here. Say we want to replace sponge Bob with something else, say Patrick or something like that. Let's create a new variable. We'll call it Pat for Patrick. It doesn't matter what we call it. We're working with our namestring here. We'll leave this. When we press the dot again, we get all these things we can do with it and we're going to double click, replace with, replace. We can replace anything with anything else. What I want to do, I want to replace sponge Bob. I want to give it the new value, Patrick. Always end with a semi colon. What that is going to do is take the name, everything inside the name, it's taking all of this, we want to replace every occurrence with Spongebob type that we want to replace it with Patrick. Then the result of that operation is stored in Pat. Then we can put Pat here. If we run the application, we can see now it says Patrick square pants. That's because we're replacing every occurrence of Sponge Bob with Patrick. And when I say every occurrence, let's try this, run the application. It's replaced every occurrence of Sponge Bob with Patrick. That is how replacement works in C Sharp. And again, you don't have to store the result of this calculation into a whole new variable. We can shortcut that, just put it there, and that will equally work just fine. You can see Patrick square pounds Patrick. Patrick Patrick. You can see that is how replacement works when dealing with strings. Another thing we can do with strings is work out the length of the string. That one is very simple. Here I have a variable called example. This is everything inside that variable to work with. Example, I put a little dart afterwards and I type length to make this quicker. You can double click this or you can press the tab key on the keyboard. That might be a lot quicker for you to enter these values in the future when I compile the application. Now we can see that this sentence here is 44 characters long. That's quite useful when you use substrings to extract certain things from a substring. Let's talk about another method called index of. Now what index of does is if you specify a word like sponge Bob, it'll actually tell you the index of where this is in the string. Rather than counting 1-234-567-8910, character position 22, for example, we don't have to count, we can actually use a method called index of. If I put index, then I want to put in, for example, sponge Bob. That will be in double quotes, because sponge Bob is a string, we want to store the result of this. Now if we hover over index of, you can see over here next to this pink cube, it says t. That means the result of this will be an integer s define a new integer. I'll just call it index. Then I'm going to output the index to the window. Let's run this real quick. You can see apparently Sponge Bob is a character position 22 here. That's 22 characters in index of is another method which is quite useful to get the index of whatever word you would like. You could put in, for example, just something like that. If we run that, it gets the first occurrence of which is this one here, 012, that's the first occurrence. Again, it has lots of different things you can do with index of, but that's an example. 9. 1-6. Working with Numbers: Okay, let's look at some examples of working with numbers in C sharp. We're going to look at multiplication, addition, subtraction, division, all that good stuff. So let's get going. Let's have a look at an addition example. So how we add numbers in sharp. We have a sample application here. We're just defining a variable, setting it to zero, and outputting it to the screen. So not really much is going on here. We're going to use our variable. I'm just going to do five plus four, which we know equals nine. I'm just going to run the program and we get nine is the output there. Addition is very simple, you can keep going with this, et cetera. Very easy. Same again with subtraction, we can pretty much do the same thing. Five minus six is negative one. You can see subtraction also very easy. Again, you can do this, mix them both. It doesn't really matter. It will work this out for you. Multiplication. Let's do three multiplied by four to multiply numbers in C sharp. Use this asterix here, the little star, and we should get 12 as a result. There again, we can combine multiplication with addition and subtraction, just like you do in mathematics, for example. Now this is where there's a couple of gotchas With division, the divide sign is a forward, let's do an easy 13/3 Let's run the application is one. Because there's one, there's 13.3 The result is one. That's how we divide numbers however. Okay? Gotcha. Number one is divide by zero. We can't actually divide by zero. You can actually see now. Anyway, back in the day a few years ago, if you did three by zero, you could run the application and you would get an error. Because it's not a realistic calculation, it can't work it out. Now we have a red line underneath, and when we hover over that, it says division by constant zero. It won't actually let us run our program, but because the variable result is zero, let's just feed that into there and run the program. And again, it errors just like it should. The first error we caught at compile time when we try and run the application, because we're using zero here, it's telling us we couldn't run the application. But when I gave it a variable which is result, which also equals zero, we can trick it in order to run the program, but we still get that error attempted to divide by zero, which we cannot do. So that's something you should always bear in mind when working with division. You should never divide by zero. When we talk about if statements in the future, I'll show you how you can protect your program to avoid dividing by zero and the other gotcha with regards to division is using decimal numbers. Let's look at a decimal number example. We're going to use a double data type here, and we're just going to initialize it to zero. Now let's just do an example. Let's do 3.45 0.6 which should work fine. You can see here, here's the result which is in decimal format. However, if we do say 200/3 this is not a whole integer number, it will have a decimal place on it. However, when we run the application, you can see it's actually doing some rounding here. It's, I believe, down to the nearest integer, which is 66. However, if we add 0.0 onto the end of these and run the application, you can see this is the true answer here, 66.666 reoccurring. Then it's rounding to seven. This is something you should pay attention to when working with decimal numbers. C sharp will make an assumption because if you have two numbers here, this 200 is an integer, three is an integer. Neither one of these of decimals, it's only the result which is a decimal. What C sharp is doing it is saying, oh, hey, there's an integer here. Oh, hey there's an integer here. I'm going to give you the result as an integer. That's a little bit annoying. What you have to do is change at least one of these to a decimal number. When you do that, you can see we get the true result here. That's just something you should really bear in mind when working with the division of decimal numbers. The next operator I'm going to show you is the modulus operator. Let's just put this back as an integer. Now, what the modulus operator does, it gives you the remainder of a calculation. Let me do an example real quick. The modulus is represented by a percentage mark. Here, what this does, it says, how many times does three go into six? Well, three goes into six twice and then there's no remainder. The result of this will be zero because it's the remainder of this. Again, if I do 22 goes into 63 times, perfectly again, there's no remainder. However, if I put four here, four goes into six once. However, there's a remainder of two, so this will be the result two. What modulus does, it gives you the remainder of a calculation. After dividing this one into this, 14 goes into six once with a remainder of two. If I run the application, we get two, just like the very first example, three goes into six twice and there's no remainder, the result should be zero. Modulus is quite useful when we want to know if a number goes exactly into another number. If the result is zero, we know it's perfectly divisible by that number. That's what modulus is, or modulo whatever you want to call it. And it's represented by a single percentage, just like that. Now I want to talk about the order of operations when working with multiplication, addition, subtraction, all that good stuff. Let me show you an example. I have result, which is our variable five multiplied by four -2/7 I want to add on the result of five plus one. Let's have a look at this example. If you've done a lot of mathematics in the past, then maybe you can skip over this section. It might be quite obvious to you, but C sharp works pretty much exactly the same as mathematics in the real world. If you've ever seen these things on Facebook or Instagram, and they say, oh, what is the answer of this? And people are giving all the wrong answers because they don't understand the order of operations. Here we have this thing in mathematics called bid mass or Bodmass. Let me show you that now. Bid mass, some people call it Bodmass. It doesn't really matter. The only difference is the I here and the o here. But they mean the same thing. So the first thing is brackets. If we have a calculation like this, anything inside the brackets happens first. Five plus one. That happens first, which is six. And then we can remove that and that gets replaced by six. The next thing that happens is the I or the o that's to the power of, or the square root of. We don't have any of that stuff in here, so we can skip that. The next thing is division. The division happens next, and that's 2/7 Now, I'm not sure what 2/7 is, it's a decimal number, but that will happen next. This calculation here. The next thing that happens is multiplication. This right here, this will get worked out next five multiplied by four, which is 20. Then any additions after that, then the result of that will get added to six followed by subtraction to the very last thing that happens is this one here. That's the order in which this is calculated. It doesn't happen from left to right. Five times four takeaway two. It always happens in the order of the symbols, just like mathematics. For example, if we run the program, well, it can all get worked out. For us, the result is 26. That is the order of operations. Something just to bear in mind when working with this in C sharp. The last thing I'm going to talk about to do with working with numbers, is two to the power of two, which is four. If you're not very familiar with mathematics, the power of just means how many times it's multiplied by itself. Two to the power of two is the same thing as saying two multiplied by 22 to the power of three basically means two times 22 multiplied by two multiplied by two. Again, that's what the power of. The reason I'm showing you the power of is because the power of doesn't have a symbol like multiplication or subtraction, we have to utilize what's called the math namespace. Now let's look at that. Now if I say result, which is the variable we've defined here, then I say math MAT H with a capital M. When I press the period symbol here, there's lots of different things we can do. All these are built into our C sharp library here, and we can use any of these. Look, the sign, cars, tan, truncate, logarithm, all this fancy stuff. But what I'm just going to use is power, which is represented by POW. If we open brackets here, it's asking for our first number down here, it says a double precision floating point number to be raised to a power. Let's say we want to look at two to the power of two. It's asking for a double, which is a decimal. I'm going to put 2.0 because it wants it in decimal format. I want to raise it to the power of two again, end it with a semi colon. Two to the power of two is saying two, multiply by two. The answer should be four. You can see here the answer is four. If we want to do two to the power of three, it should be eight. You can see where this is going, 163264128. There you go. That is how to do the power of, but not only the power of. You can actually utilize a lot of things in this math class here, all different things here. But that is an example of how to use the power of, and working with numbers in shop. 10. 1-7. Getting User Input: Let's take a look at interacting with our software. For the most part, when we run our application, so far we just can see results on the screen. But now I want you to interact with your software. You can give it some information. For example, let's take a look at how to do this with a console application. Right now we have a sample application, It's just printing what is your name to the screen. When I run that, it's just saying what is your name? I want to be able to type my name in here, for example, Robert. And then when I hit Enter, I want it to say hi Robert, for example. Something like that. We can utilize the read line line right here. So far, we've only used this line just to halt the application, so our window doesn't close on us. Because remember, without this, the window just instantly disappears. However, it does have a function, what read line does. It actually captures some input from us. What happens if we hover over this? It actually tells you it reads the next line of characters from the standard input stream. Quite complicated isn't What this basically does is captures our input when we hit the Enter key on the keyboard. The result of that we can store into a string. If we harver over this, you can see string here. This is what comes back to us. We can define a new variable. We'll call it result. We could call it user input. We can call it whatever we would like. What we're doing now, we're getting the result of this operation which is read line that grabs anything we type in there after we hit enter and it stores it in this variable here. Then what I want to do is say hello to whatever name you put in here. Remember how to concateinate strings. We have our first string here, hello. Strings are enclosed by double quotes. Then we want to join a string with the result of this operation, which is also a string. We're going to do that there. We want to sound really enthusiastic. We're going to do an exclamation mark as well. We're joining three strings together. Hello, the exclamation mark, and the result, which is a string variable from the result of the user input. Let's run this application. Now it's saying what is your name? I'm going to put Robert. When I hit Enter, we have nothing that is because we haven't told it to keep the console window open. Let's put that back down there again. Hit the play button, type in our name, Hit, and now it's saying hello Robert. It's quite easy, isn't it? And that's how to capture user input in a console application. 11. 1-8. EXERCISE - The Number Multiplier Game: Okay, let's look at a quick example now. A little practical application to test your knowledge of working with numbers in C Sharp. I'm also going to test some of the knowledge you've learned so far. And I'm going to introduce the concept of converting data types, converting a string to an integer. Let's take a look at this now. So what we're going to do, we're going to build a sample calculator, but our calculator is only going to multiply two numbers together. It's not a very fancy calculator. Let's start here. We're going to say welcome to our number plier. We want to tell the user what this is. We're going to say, oh, hey, welcome to our number multiplier. Then we're going to ask for their first number. This is the first number, they're going to multiply to another number. What is your first number? We're asking the user what their first number is. To grab user input, we use console read line. Then the result of this we need to store in a variable, we'll call that first number. Now first number will hold the user's first number. Now immediately you see this red line underneath console read line. If we hover our mouse over that we can see here cannot implicitly convert type string to int. What it's saying is, okay, look read line gives you a string because we're asking for the user's input. And they could put a sentence, they could put lots of letters. We don't know what the user is going to put in here, basically, but we actually want an integer from this. The user could type hello and we're trying to put hello into an integer, so there's going to be a problem there. What we want to do is use the convert library. What that is, if you type convert to a capital C, press period there, do we get lots of options we can do here. What convert does? It gives us a lot of different methods of converting data types. What we want to do is convert a string because that's the user's input. We want the result as an integer, which will be our first number. When I press here, what I want is two int int 32. Perhaps I haven't explained this yet, but a standard INT is also considered int 32. It's a 32 bit integer. You can have a longer integer which supports more digits or even a smaller integer. Int 32 is a standard integer in C Sharp. When I open parentheses on this, it's asking for a string value. This is the string it's going to convert to an integer and our string value, well that's the result of the user input. That's console red line. We'll put that there. We'll close our brackets and we'll put a Sami colon. Now you can see the red line has gone. Similarly, you could just store the result of this in a new variable, a string variable, and put that in here. It doesn't really matter, but we're doing it all on one line. Now what we want to do next is grab the second number from the user, the second number. That will be a new variable called second number. We want to ask the user what their second number is. Now we have the user's first number in this integer variable here, and the user's second number here. Now we want the result of that, that will be the result of the calculation first number, remember multiplication is the asterix second number semicolon. Then we want to tell the user what the result is. Let's do that. We're going to say the result is, then we're going to concatenate the strings together, which is result. Then we want this so the window doesn't close. Let's run the application here. Look, welcome to our number multiplier. What is your first number? Why not number four? What is your second number? How about number five? And that should equal 20. It says the result is 20. Pretty cool, isn't it? Again, we can use different numbers in there, but that is a very simplistic view on how we can get user input using console read line, how we can convert data types. So we're converting a string which is the user's input, an integer which is our variable here. Then when we multiply our integers together, we get the result and we're just telling the user the result. That is a very simplistic way of working with numbers in C. Sharp. 12. 2-1. Methods: Now I want to talk about methods in Sharp. We've actually used a lot of methods so far. For example, right line is a method, read line is a method to the power in the math helper was a method. Now we're going to create our own method. When creating methods in C Sharp, they all have a purpose. If you have a job which is usually done more than once or a complicated job, you can put it in a separate method. When I say method, here is an example of a method here. This is the main method. Everything within this method here is within these curly braces. Here, the main method is a special method when our software is executed by default. The.net Framework, which is everything C Sharp is built around, this looks for a special method called main, and it has to have this name. And all method names are unique, so they can't have the same name, just like variables. Once it's found the main method, it runs all the code within these two curley braces. Here, the only code we have are two lines right here. When we run the application, we can see Hello World. And the next line keeps this window open for us. Now let's look at creating a brand new method where it says static void. I will cover that in a later tutorial. For now, let's keep it very simple. After we write static void. In this case, we want to give the method a name. Now remember I said methods must have a purpose to keep things organized. Generally, they should have a purpose. Our new method, what I want it to do, its purpose, its job is to say hello world to the user. That is the only thing it's going to do. Now I know it's function, what it's aiming to do. I can call my method with a name that makes sense to words. I'm going to call it, say hello world. That's going to be our method name. Now the next section are what's called parameters. I'm going to talk about those later. I'm going to keep it simple for now. Do an open parenthesis and a closed parenthesis. Next, open curbrace and close curbrace. Just like that, you can see it can mimic this. All our code for our method will live here in this highlighted section between this one and this one. All our functionality for this method lives here. We want to say hello world to the user. Well, we know how to do that, We've covered it before. That is this line of code right here. Our method say hello world. Its job is to say hello world. So that's going to print this to the black window easy. Right now when we run our software, well, it's not actually going to do anything. Why is that? That's because the main method is run by default. So this section here, and this is the only thing which is going to get run from our main method. We know nothing of this. What we need to do here is say, oh, hey, can you run our method in order to run our method? We just do that. When we launch the application, the main method is run. It goes down, this line is executed. When this line is executed, the code goes into here. This line is run. The method has finished its job. It goes back out to here, and then finishes off with this section here. When you have a method, it goes out, then back in again, and carries on. If we run the application, now we can see Hello world. That's because we're now calling our method. Just to recap if I went too fast or it's complicated without this line, our method will never get executed. When we run our software, we can create lots of them. 3,000 5,000 1,000 Again, they all must have a unique name. But when we run the software, none of this will get executed. And that's because we're not actually telling the computer to actually run them to run a method. Again, we do this again if we want to run this method, very similar, et cetera. This is how to run the method, this is how to define the method. And that is a very simplistic view on how we can set up a very simple method in C sharp. 13. 2-2. Method Parameters: Now I want to talk about method parameters. A parameter is just a fancy way of giving a method some information. Here you go. Here's some information. Work with it. We're going to use an example. Here's an example. We're just saying hello world to the user. Very simple. But what if we want this method to say hello John, hello Harry, or hello Roberto? These names are something the user can provide to us. Here's an example. We're going to ask the user a question. We're going to say, what is your name? What your name. And then we want to get the user's input which is console dot read line. That's how we get the user's input. And we store this into a string. I'm just going to call it name, asking for the user's name. The user types some information and we're stuffing it into a variable called name. Now, our method here, I want to say hello, and then I want it to say the result of this variable, which is going to be the user's name. We don't know what that is. The user can type anything they want. Now, the job of this method is changed. I don't want it to say hello world. I want it to say hello to the user. Now I'm going to say hello user. Its job has changed when I called the method. Again, we need to make sure that matches up in here. It's no longer saying hello world. I want it to say hello to the user's name. That's our variable called name. However, look you can see there's a red line under here. And that's because our method here is isolated from this method. It doesn't know about this variable because this has been defined inside this method, this method, it doesn't actually know about it. That's how we can use parameters to solve this problem. What a parameter is, we can define them within these brackets. Right here, we're going to type string name. Now you can see this red line has gone away. Every parameter you put into a method here goes inside these open brackets, you can see this main method. Now this section right here, well that has one parameter, it's had one parameter all along. Again, when we define a method here, we can add our own parameters. I've added what's called one parameter and it's called name, it's a type string. Now, inside this method, we're using this variable, this parameter, when we call our method from the main method. You can now see there's a red line here. When we hover over that with our mouse, you can see there is no argument. Now, argument is synonymous with parameter. It's the same thing. There's no parameter given that corresponds to the required parameter name. It's basically saying, now this method needs a string. We can't call it like this anymore. What we do, we take our name variable, which is the result of the user's input, and put it into there. And now you can see we're collecting the user's information. We're giving this user's information to our new method called say, hello user. So we're giving it the user's name. Then the code goes into here. Name now equals the value which is being passed into it. And that's our parameter. Now we're using our parameter by outputting it to the black window. Then the code execution comes back out. And then we're keeping the window open again, just so this isn't confusing. We could call this whatever we want. We could say name of the user. We could call it ham sandwich. It doesn't matter. You can see the red line here, because it needs to be the same. But you can see here, this doesn't have a red line. And that's because we're actually defining it right here. Even though the value comes into the method here, when we arrive in here, we can call this whatever we want. It will still have this value, but it doesn't need to be the same name, like this. It doesn't need to be like that with the same exact name. It can be, but it doesn't have to be. That is something you should bear in mind. When the parameter is passed in, the value is passed in, it's redefining a whole new variable here. But with this value, I hope that makes sense when we run the application. Now we're saying, what is your name? Roberto. Now you can see it says hello Roberto. We can run this again. We can say hello Henry. That is how parameters work in a very simple view. One last thing, We don't have to have one parameter. We can have a lot. We could have another one of a different type like age, which is an integer. Now I want to ask the age of the user. What is your age? Remember, age is an integer because it's a number. I'll just call it age. Now we have the red line because this gives a string and we want to put it in an integer, which isn't going to work, but we covered this before. We're going to use, we want to convert it to an integer which is 32 bits and then put the parentheses around everything. Now we've converted the string from the user to an integer. We're putting it into an integer variable called age. Now we have our red line again, that's because we have two parameters on our method. Now, name one age. When we hover over this red line, you can see it now requires a string and an integer. When we call this method, we need to add this information here, and we can use a comma. Now it's even asking, it's even telling us what we need. Age, we take our age, put it here. Now we have a method with two parameters. And we're passing two parameters into it. We're not doing anything with it now. Let's do something with it. We're going to say age is age now when we run the software. Let's do that. What is your name? Harry. What is your age? I am 67 years old. Hello Harry. Your age is 67. Again, we can have ten parameters if we want. We could have different data types in B, all different kinds of things. Again, if you want to add more, it's just another and how you pass them in. Again, you use A here. This is how parameters work generally with methods in C. Sharp. 14. 2-3. Method Returns: Let's talk about getting information back out of a method. In order to do that, we use the return keyword. Let's look at returning information back out of a method. We have a sample application here. It's asking for the user's name. It's storing the user's name in a variable, then it's saying hello to the user. What I want to do now is create a method whose job it is to ask for the user's name and get the user's name and give it back to us. That's what we want to do. Now, in order to do that, we're going to create a new method. The easiest way is to copy this one, delete everything out of it, and give it a unique name. Its job is to ask for a user's name. We know how to do that. We have it right here. We're asking for the user's name and we're storing it in a variable here. When we talked about parameters before, that is how to get information into a method. We define them here and we pass information in from main. However, getting information back out of main, that is what we're looking at right now, and that's called the return keyword. We're returning information back out of a method, so we can use it here. When we launch our application, we're going to ask for a user's name. We get the user's name, put it in the variable. Now we need to throw the user's name back out of here and then say hello to them. Right now, we can't do that because it doesn't understand what this variable means, because it's defined in our method. So we need to get this out of here and define it here. In order to do that, we set up what's called a return data type by default. Here you can see there's one on main even and one here. It's called void. Void is like a black hole. It's like nothingness. It's nothing. But what we want to do is return our string variable here, back out of the method. We replace our nothingness void with string. Now we've set up a return data type here for this method, a string, and we want to return this variable here. What we do, we take our variable, we use the return keyword. We enter a white space, put our variable, and then all lines with a semi colon. What is happening here? We're asking for the user's name, we're stuffing it into a variable, and then we're returning the variable out of this method. You can see when we return the variable here, this variable is of data type string that needs to match our method header, which is all of this line right here. So you can see we're returning a data type string, which is our variable here. Now back here, we're going back into our main method. We're calling this, but we're not actually getting any information out of it. We've actually done this before. You can see console dot read line. This is a method and we're actually getting information out of it. And that's exactly how we do this. We can just do that and everything works again. Remember before when I said this doesn't need to be the same as this, we could just say name for example. You can see it still works because main only knows about anything defined in Maine. Ask for a user's name, only knows about things defined in here unless you pass a parameter in or return something out. Let's go over this one more time. Actually, let's run the application. So we can see we're running the application. What is your name? Bob. And hello Bob. Quite easy? Well, it looks easy until yes. Let's look at what's happening one more time so it makes perfect sense. We're running the application, we're asking for the user's name. So the code execution goes here, there's no parameter, so we carry on. What is your name? The user types their name, here, we're storing it into a variable called name of the user. We're returning this information back out of the method, which is then stored in name. That's the result of this method. Name of the user, We're returning it, It's the result of this method now that is stored in this variable called name. We're then just outputting the name to the black window and then keeping the black window open. That is how returns work with methods in C Sharp, remember parameters get information in and returning gets information back out. 15. 2-4. Method Overloading: Now we're going to take a look at something called method overloading. What does that mean? Let's take a look at this example. Here we're defining two variables here, both of data type integer called number one and number two. What we're doing, we're calling a method called ad, which we've created here. It takes in two integer parameters, and it's just adding the numbers together. It's returning the result, which is an integer back out here. And then we're outputting the result to the screen. Very simple. The answer should be 20 2022. We have the correct answer. What I want to say now is what if I want to add two doubles together? Let's turn these integers into doubles. Now I have two doubles here. This could be 6.4 and this could be 16.2 for example. You can see now we have a red line under here. Because our parameters are integers. It's expecting integers in here. But we still want this method, we still want to be able to add integers together. I guess what we could do is have a method called in, and then maybe another method called a double, for example. And then this would take two doubles. Then the other one would take two integers, for example. That's how we could get around that problem. Then obviously, that would have a return type as a double. You can see where this is going, but what if we want to add, for example, two decimals together or two floats together? Then you can see we're going to have to have a method for each one of these. That is quite tedious and it can really bloat out our program. But what we can do is use something called method overloading. What that does that allows us to have one method but give it different parameters but with the same name. Now, a method can have the same name only if the parameter data types or the number of parameters, for example, are different. Let's go back to our previous example where we were adding two integers together right here. What we can do then is copy this method. We retain the same name, for example, but in here we're actually adding two doubles together rather than two integers. You can see what I have here now is two methods with exactly the same name, except this one takes two integers and returns an int. And this one takes two doubles and returns a double. Now when we actually call our method here, if I just open these parentheses here, now we have these little black arrows. We didn't have this before because we only had one method with one set of parameters. And I'll show you that now. If I open the parentheses here, you can see there's no black arrow. We only have one definition for the method add. But as soon as I add the second one right here, now we have more options available. Now we can add two integers together and we can also add two doubles together. This is an example of method overloading in C Sharp. It just allows you to have different options for a method with the same name. You can see C Sharp has built in methods that take advantage of this already. For example, when we write something to the console, you can see if I do the exact same thing, this method is actually overloaded 18 times already. So you can see it's quite a popular principle in shop programming, so I hope this helped you, and this is an example of method overloading in C shop. 16. 3. Comments and XML Summary Tags: Now I want to talk about something very important. If you want to make your life a lot easier or you want to take programming more seriously, then you need to be using comments. So what are comments? If you have a very complex application or a very complex line of code, it's really long and maybe you knew what it meant at the time. But if you come back to this a year or two later, you might have totally forgotten what it meant or the craziness you were typing at the time. So that is why comments are very useful. It's a reminder mainly to yourself, but if you're working with a team of people, it also tells them what the code does without them having to read and understand all the complexity. We can do comments in three ways in C Sharp. The first one is a one line comment. We could do that. For example, you can see when I leave a comment, it's green. Now, this comment here, it does not get run by the software when you produce your software, like an EXC for Windows. It doesn't get compiled into it, so you don't waste space or megabytes with the comments. These are really useful. Again, if you have something really complex, it just tells you what the next line does. So we can put comments on pretty much any line we want. We can put them after a line. Again, they don't get run, so there's no red line underneath. And it just really tells you what the next line does. Generally, people put the comment above the code and not next to it, but you can put it next to it if you wish. Let's just put some comments here. You can see roughly how it works here. I'm going to say, we know this line keeps that black window open. So I can put a comment that says it keeps the window open. This one it says say hello to user. I could put a comment that says say hello. When I come back to this a year later, and I've forgotten everything about shop, because that always happens with languages. You can open this and instantly know what each of these lines do. You don't want to go crazy with comments. You don't want every line to have a comment. But definitely if you don't understand something, then definitely put a comment there because it will remind you again and you can get back into it a lot quicker. That is a single line comment. The next thing you can do is a multi line comment that is one forward slash followed by an Asterix. Then if I press Enter, you can see it creates Asterix is on every line until I end it with one more forward slash. Now anything I type here is all inside the comment. This is useful when you want to introduce maybe a method or what's called a class. This is the whole thing we're working with right now. Say you're working on a team of ten people at the top of the file. You want to say who made it, because if there's a problem, then they can say, okay, Bob wrote this whole section of the software. We know because the author is Bob, then Bob, when he makes this part of the program, he can say, I made this, don't hate me. Then he can summarize what it is. It's a music player, It's great, anything he wants in there. So it's really up to you. But this is how to do a multi line comment. They are useful for sort identifying maybe who wrote the file and maybe roughly what it does. That way people don't have to read every method and try and work out what this file does. Generally, multi line comments go at the top of files, may be up here, so the first thing people can see or it can go above something very complicated, like a method or something like that, that's generally where people would use a multi line comment. When you want to write a lot of single liners, for example, the last comment I want to talk about is what's called an XML summary tag. Now it's not really like a comment like this per se, but it gives you important feedback. It gives you in plain English feedback on what maybe the next line of code does. But we can use these for maybe methods or things like that. If you have a complicated method, maybe it's like 100 lines long, it does all this fancy stuff. Maybe the name of the method doesn't really do it justice. It might say ask for user's name, but it does lots of other stuff in there. Maybe it returns something that might be a bit complicated or it has lots of parameters and you might not know necessarily what they mean. We can use what's called an XML summary tag to expand on this, where I call my method. Here I hover over it with my mouse, you can see it doesn't really say much. It says string. Program, do ask for user's name. However, if I har over this one console dot read line, look at all that information there. It's saying reads the next line of characters, it's telling me what it returns. It's lots of different information. I'm thinking, oh, well, where's that on mine? How do I set that up? And that's what's called a XML summary tag. Above our method here, do three forward slashes 12. And when you do the third one, it creates this nice little template for us. It's in XML format. Here's the open summary tag, here's the closing one that represents the information here which says, reads the next line of characters from the standard input. Here I define roughly what this method does. If someone hovers their mouse over here, they can quickly see what it does without having to read 100 lines of code. For example. It's giving the other developers information on what this method does. For example, you want to give it a very descriptive thing. Now when I hover over this, oh, okay. It asks for a user's name. Oh yeah, I forgot I built a secret Bitcoin miner in here. So for example, you can put whatever you want in here, but it's for your benefit. Imagine you put your software away for ten years. You come back ten years later. You've forgotten everything. But now you can just simply have your mouse over here and oh, that, yeah, of course, I forgot about that. So it's good for your benefit, but it's also good for other developers, maybe on your team. For example, inside here we have two returns tags. And that's just roughly what's being returned. So we're returning the name of the user. Remember it's, you can put a little hint in here when we get the user's name, we're saying, oh, remember it's only their first name. When we hover over here, we can see it returns the name of the user, but we're reminding ourselves, it's only their first name. This is why these XML summary tags are useful, because when you hover your mouse over here in an instant, you know exactly what it does in plain English. So these are really useful. And you can see this method has a one parameter here. When I do the same thing here, we have an extra thing here. Again, we can use our summary. It says hello, say hello to the user. Parameter defines what our parameter does, like what information we give to it, It will be the user's first name. This is say hello to us. When I haver over this we can see here, say hello to the user. When I open the bracket here, it's telling me what the it expects stre what is that full name? Is it first name? Last name? Nickname. But when I look down here Oh, it's the first name, of course, Yeah. Because we're reminding ourselves, we're telling our user, when we call our method, exactly what our method does, what it expects as a parameter, and also what it returns back. So they are the three different kind of comments you can use in C sharp. 17. 4-1. If and Else Statements: Let's take a look at something new conditions in C sharp. We're going to take a look at the if statement and also the el statement. E L S E for L. What a condition is something that is evaluated as true or false. Take a look at this. Are you Bob? Is your name Bob? Well, the answer is either yes or it's no. Do you have a you either have a dog or you don't have a dog. Are you six feet tall? Either I am or I'm not. So they always have a yes or no answer. The condition in this case is a Bob, that is the condition. You could expand this condition. Are Bob, do you have a dog? In which case? All of this is the condition. If your name is Bob but you don't have a dog, then the answer is no. Otherwise, it's yes if you have both, for example, because there's an end here, this is a condition. This is what our condition is. We deal with these every day, multiple times. And we can represent these in C sharp by using what's called an if statement. Let's take a look. A very simple one. We're going to create a little bit of software called Are you, Bob? What it does, It asks for the user's name. We take in the user's name. If the user's name is Bob, we, we're going to give them an amazing greeting because we really like Bob. If their name is not Bob, then we're just going to give them maybe a standard Hello, Roberto or something like that. Take a look at the format of the if statement. It starts with If, that's the keyword, the open parentheses, just like we do on a method. For example, open parentheses inside the parentheses. Here we put the condition. Our condition is, well, are you, Bob? We know that the name variable contains whatever the user entered, so we're going to put name. Then we want the equality operator that's represented by two equals sign. When you assign something in C sharp, we use one equal sign. But when we want to compare something, we use two. We're saying if the user's name is equal to Bob, then we need to do something in C Sharp. Sharp loves these curly braces. When we have a method curly brace, when we have an if statement curly brace, when we open a curly brace, we always close a curly brace. You can see these ones here match up to these ones here. That's just how the language is. This is our if statement here. This is the content of our if statement. Everything between the curly braces. Now, like I said, if the user's name is Bob, we want to give them an amazing greeting. Let's try and type English. We know their name is Bob. We might as well just put Bob. Hello, Bob. These, those name is Bob are giving them an amazing greeting. Look. However, if their name is not Bob, maybe it's Roberto or Henry, then we need to give them a different message. If we run this program now you can say, what is your name? Let's type in Henry. It's giving us a standard Hello Henry. It's actually ignoring this completely because the name is not Bob. However, if I run the application now, what is your name? Well, my name's Bob. And remember C sharp case sensitive. So we only checked for a lower case barb in our if statement, so make sure it matches that. So click Answer. Now we've got our amazing greeting look, but we have a problem Look. It also says hello Bob as well. So he's getting two greetings. And that's because the if statement condition, which is this section, is being satisfied. It evaluates to true. Therefore, this line of code is getting executed. Once the if statement ends, we're still executing this bit. But maybe we want to reserve this greeting for Henry, for example. Therefore, we introduce what's called an L statement. E LSE, again, curly braces. This section is reserved for Bob. This section is reserved for anything not Bob. This evaluates to true when the user's name is Bob. It evaluates to false if it's anything else. Else, all the else stuff goes in here. We want to give the standard greeting to anyone apart from Bob. And that is how the else statement works. So if this is evaluates to true everything here, If it evaluates to false everything here, for example, if I run the program, now what is your name? My name is Bob. Now I get the standard greeting, and this section is ignored completely because my name is Bob. But when I run the program, now I type in anything, we get the standard greeting because this part is ignored, it falls to the else section here. It cannot exist without an if we can't do this, that won't make sense. Else always needs an if to go with it. When we try and run it, there'll be an error. You cannot have else by itself. It always needs an accompanying if above it. It's a very simplistic view on an example condition, which is the if condition in C. I want to just run through a quick example so you fully understand how these conditions work. Now, when you have an if statement, it has a condition and an action. If this evaluates to true, it runs this section here. If it evaluates to false, this section runs here. When we talked about variables, we had a bolen variable. Bolen variables evaluate to either true or false. What we can do, I'm just going to use parentheses. Parentheses is optional, but I think it improves readability. Now we're storing the result of this into a variable called is Bob. Then we can put is Bob right here is the name given by the user Bob. And when I say is, I mean, is it equal to the equality operator, yes or no, true or false? Then true or false is going to be stored in this variable called is Bob. If statement is then ran, it's going to say is true false. If not false. If I run the software here, I type in Bob, hey Bob, you're amazing. It's exactly the same thing. It gives you more clarity on what is going on, if that makes sense. I haven't talked about Booleans that much, but it's basically saying, does this equal to true or false? And this is either going to be true or false because that's how you represent it as a booling. And then when we run the if statement is Bob will be either true or it will be false. And it's going to run the appropriate one. If we're not Bob, we're Henry. Then it's going to say, hey, random person. 18. 4-2. Else If Statements: Now let's expand on our if condition example in our last tutorial and talk about the el if clause. Here we have our standard greeting for Bob. But what if we wanted a special greeting for Henry? Bob gets his own custom message. Henry might have his own custom one, then everyone else gets a standard one. For example, here we introduce the else if statement. Let's go down here. This is denoted by that we want to change Bob, because we already have that condition. These conditions really kind of really need to be unique. Otherwise it won't make sense. It'll be redundant really. So now we're saying, are you Bob or are you Henry? Remember, let's make our comments make sense. So, is your name Bob? Hello, Bob. Is your name Henry? Oh, hello Henry. But he gets more exclamation marks because he's caller. Then if you're not Bob, you're not Henry, then you are everyone else at the bottom. So let's type in Henry, for example. Now we're getting the Henry one because our name is Henry. Very simple. Once you understand how the if and the else works, else if is just something else. Again, we can even expand on this and have another name in here, maybe Scott or something like that. You can modify that appropriately to whatever you wish. That is how the elif statement works. Again, you don't need el, you don't need else. If quite happily have this for example, If I type in anything else, they're not going to get a message at all because we haven't told it to do anything. That is the power of the el if statement when using the if condition. Now I'm going to show you a little bit of advice. Now, we've covered if el if statement. That is, when you have a condition, for example, with only one line of code underneath. So we have this condition, one line of code. Then this condition, one line of code. When we have one line of code, then these curly braces here, they're optional. What that does by removing those, it increases readability. It gives less bloating to your software. This is exactly the same as what we had before. However, for example, if we have two lines of code or more under each condition, then there's a problem. And that's because it needs those curly braces. Right here you can see there's a little red line there, and the error is not very descriptive. That's because it's trying to read all of this on one line and it's going to throw a mysterious error. When you have one line of code under each condition, then the curly braces are optional. But you cannot do this with methods, for example. Only things like if, else, if, else, and some other things we haven't discussed yet. But that's a little tip where you can improve your code readability moving forward. 19. 4-3. Equality and Inequality Operators: Equality and inequality. What are those? What does it mean? Well, these are things you might hear now. And again, we've already covered equality a little when I was discussing the if statement. But equality is basically saying is something equal to something else. And that's represented by two equal signs here. But how do we say inequality? Okay, What if the name is not Bob? How do we represent that? What we can do there is use the not equal to, which is represented by an exclamation point followed by an equals sign. Now, it's pretty much reversed, this whole statement. If the name is not equal to Bob, then well, this isn't going to make sense now because their name isn't Bob. What we can do now is say, hey Bob. If I run the software now, what's your name, Bob? Nothing's going to happen because we haven't told it to do anything. But if I run the software and put anything else, it's going to say, hey, you're not Bob. But if I just flip this operator into an equality symbol right there, it's going to reverse the whole meaning of the whole statement. You can see now it doesn't make sense because even though the name is Barb, it's still running this. If you want to say something is equal to something, two equal signs. If you want to say it's not equal to, then we need not equals, which is exclamation and an equal sign. 20. 4-4. Comparison Operators: Okay, comparison operators. I have a very simple application here. It asks the user for a number 1-10 It takes the user's input, converts it to an integer, and puts it in a variable called number. That's pretty much the only thing this does. What I want to do, if the user enters a number lower than a five, I want to say a message to the user to tell them you chose a low number. Otherwise, you chose a high number. Very simple. In order to do this, we need a condition we're going to use. The condition we're going to say is the number less than five? How we represent less than is a left angular bracket, that looks like that, and then five. Then with the statement, we use our curly brackets. Then this is what happens when our number is lower than a five. We're going to tell the user, I don't know, you picked a low number. Something like that. However, if the number is not lower than a five, well then we can use L just pretty much reverse this. You picked a high number if we run the application. Now pick a number 1-10 Remember, lower than a five is low, so I'm going to do four. I picked a low number, and that's it. Great piece of software, isn't it? Then if the number is five or higher, let's do a five. It should tell me I picked a high number, I picked a high number. Similarly, if I put 1 million in there, it's going to say I picked a high number. But this is an example of a comparison operator that is called the less than operator. Similarly, we could use the more than operator, which is represented by a right angular bracket. Now, this is not going to make sense. We'll have to reverse these. That's going to do exactly the same. But you can see it's reversed. If the number is more than five, then we picked a high number. Otherwise we picked a low number, it's going to do exactly the same thing. But because I reverse to this, I have to reverse these two. It only makes sense the other two are more than or equal to, and less than or equal to. More than or equal to is represented this way. More than or equal to, less than or equal to, as you may have guessed, a left angular bracket and an equal sign when using things like not equal to, less than, equal to, more than equal to, Try and remember that equal sign always goes on the right hand side, always in C sharp. Now, if the user picked a number less than or equal to five, then apparently they picked a higher number, which isn't true. We reverse these again. Okay? Less than or equal to five, they picked a low number, we had less than five before. If it's anything up to number four, then it's a low number. If we want to say less than or equal to that, we would need to do that instead. Because the number is less than or equal to four, then it's a low number. Less than or equal to four is the same as saying less than five. Again, we can use more than or equal to reverse the logic. Again, if the number is more than equal to five, again, we can reverse these statements, we get exactly the same thing they are what's called comparison operators in C Sharp. If we put seven, you picked a high number. 21. 4-5. Boolean Operators: Booling operators. It sounds a bit complicated, but I assure you it's not. A booling operator is basically a way of saying and quite hard to say. What we're going to do is create a sample, a basic lottery application. We're asking the user for a number, 1-10 If the user enters a three or seven, then they won, they've won the lottery. Let's have a look out, we can implement this. If you say the sentence out loud, it's pretty much telling you what you need to do if the user implied picks a number which is three, a quality for three now. Or is represented by two vertical pipes like this, 12. I don't know why. That's just how it is. The number is equal to three, the number is equal to seven. It's very simple. When you say out loud, it's pretty much telling you what you need to write. Then I want to tell the user they've they've won the lottery, they've picked the lucky number, So let's take a look at this. Pick a number, 1-103 you've won, let's prove it's not a fluke side bin number two, nothing happens, that's because we haven't told it to do anything. That's a very basic example of using the operator. You can use more than one. You can use four if you would like. So if the user picks 34 or nine, for example, perfectly works. Now you have four lucky numbers. That's the operator, what's called a Bolen operator. The other Bolen operator is the opposite. It's the one and that's represented by, to a persons that one makes more sense. At least that means, but you need two of them. With the end operator. What we can do, we can say if the number is not equal to two and it's not equal to seven, for example, then they've won. What we can do if the number is not equal to two, the number is not equal to seven, because 2.7 are bad numbers. If you choose 2.7 you've lost everything. For example, as long as the number is not two and the number is not seven, then you've one. That's how you can use the operator and you can see the logic reverses to the one we've just used with the Or operator. Now using not equal to, but the same logic applies when we run the application. Now as long as we don't pick two or seven with one, let's pick four. You can see with one. However, if we pick two or seven, it's not going to do anything because we haven't told it to do anything. That's a very basic example of using booling operators like the R and the end. Again, with these you can expand it and do four numbers if you wish. And what we can do with and operators, we can combine them as well. Let's look at a quick example of how we can combine. And let's ask for the user's name. We're going to ask for the user's name and take the user's name in. Now let's pretend that Bob only has access to the lottery application that we're doing here. He's the only one with the authority to play the lottery. What we want to do is say is the user's name Bob, does he have the number two or seven? And that's an example of how we can use and together. But the point is the whole thing will either evaluate to true or false. That's the main point of the condition here. Is the name equal to Bob and does he have the number two or seven? So I'm going to put two or seven in parentheses here. So it's actually a lot more readable and it's going to make sense. And it's going to calculate correctly as well. So, is the user's name Bob? Yes. Does Bob have the number two or seven? Yes. Let's say he has seven then he's one. Let's say the person's name is Henry. Okay. Is the name Henry? Is the name Bob? No, it's Henry. Okay. No, then it's just going to skip down here, So let's test the theory. So what is your name? Henry. Then let's put a now let's put the lucky number. I think seven is one of them. Then nothing happens because it's not Bob. Only Bob has permission to potentially win the lottery here, let's put Bob in, let's give him a lucky number and he's one. Just like that. Let's do Bob with an unlucky number, which is definitely 44. Nothing happens. You can see this is how it evaluates this whole condition with an and booling operator and also an one. It's good to use parentheses as well, to make sure a, it calculates correctly, and two, it improves readability as well. 22. 4-6. EXERCISE - Building a Calculator Game: So we're going to do a little bit of an exercise now and test your knowledge on some of the things we've learned so far. What we're going to do is create a sample calculator in C Sharp. Right now, there's not much going on. We're just saying to the user, welcome to our call calculator. And when we run the program, nothing is going on. So we need to program that ability, what the user is going to do. They're going to enter their first number, which could be a decimal, and then they're going to enter an operator plus minus multiplication or division. And then they're going to enter their second number. And then it's going to perform the calculation and display on the screen a few things to consider. Number one, the user can enter decimals. We need to make sure we convert our numbers to doubles, for example. The next thing is we need to take in the operator that the user enters and work out whether it's a plus, minus, divide or multiplication. And then act on that appropriately using conditions. Let's ask the user for their first number. We know how to do that. We're asking the user for their first number. To collect that information, we use console dot read line. We want to put this into a double. I've set up a variable called first and that will store the first number, but console dot read line returns a string. We need to convert this string into a double. We can use convert to do that, we type convert period and we want to double open brackets. Put the output of this inside the brackets. And then remember to close the brackets. Now we've captured the user's first number. The next thing we want to do is take in the user's operator, but let's take in the user's second number first. That's because we can just copy and paste this. It's a lot easier. We have the user's first number and the user's second number easy. Now we want the operator. Let's copy this. The operator will be a string because console dot read line already gives us a string. We don't need to convert anything so we can remove this. We're going to create a new variable called operator. But look what happens when I do that. You see it's highlighted blue. It's throwing an error. Why is that? That's because operator is a key word in C sharp. It's already actually used. For example, we can't create a variable with the name of double for example. It does exactly the same thing. That's because it's a reserved word. We need to choose a name that's not operator, because operator is already used in the C sharp language. I'm just going to call it OP. You may discover that I thought I'd tell you the information now. Now we want to ask them for the operator. We might want to tell them what they can do. We're saying you can choose plus, minus, multiplication or division. We're taking in the operator and storing it in a variable called p. Now we have all the information from our user. We have the numbers and everything we need. Now what we need to do is find out what operator they're using and then perform the calculation. How do we find out the operator? Well, we can use if statements to do this. We say if. Now we use the equality operator. Is the operator. Because the operator is a string, we use double quotes. Is it a plus? The code inside this, if we put in the curly braces, if the operation is a plus, we say f plus second. But we want to put the result of this in a variable. Let's define a variable which stores our result. I'm just going to initialize it to zero. Remember the semi colon result equals the result of first plus second, because we're working with the plus operator. However, what if they want to multiply two numbers, for example, then we need an if the user enters multiplication for example, then this isn't true, it evaluates to false, then the code execution will jump down. We need to catch that here in an else. If, if the user wants to do a multiplication, then we check for that. And then just multiply the numbers together. It's very easy, isn't it? You can see where this is going now. Mi takeaway and division, the division here, and the takeaway here. This is how we actually detect the operator here. In every case, we're doing the appropriate calculation depending on the condition, then always putting the result in the result variable here. The last thing we want to do is tell the user what the result is. You can see here a visual studio is offering me this. I'll take it, Press Tab on the keyboard, and now it's written for me. Now I want to tell the user what the result is. Result, something like that. Let's run the program and see if it works. Welcome to our cool calculator. What is your first number? Three, What is your operator? You can choose plus, minus, multiplication, or division. I'll choose multiplication. What is your second number? Because we know three times four is 12. I don't need to think about it. The result is 12. Well, that works. Let's try one more. Let's try 200/3 because we know three doesn't perfectly go into 200. So we can test that. Our result is actually giving us a decimal. You can see the result is 66.6 6667. So we have a nice degree of accuracy here. By using doubles rather than integers, we can deal with decimal values and numbers that aren't integer numbers that aren't whole numbers. This is a very quick example on how to make a prequal calculator in C Sharp by using everything we've learned so far. 23. 4-7. Switch Statements: So I'm going to introduce something now called a switch statement. It's a new kind of statement that we're going to learn about. And it's very similar to the if and else if statement in the way that when the if statement is run, it evaluates a condition. If it's true, then it'll run the action below. If it's false, it'll go to the next Els if statement and try that again. If this is true, it'll run this action, et cetera. Switch is very similar to this. It's just another way of representing the same information. What I'm going to do, I'm going to rewrite this as a switch statement so I can show you exactly how that works. With a switch statement, we use the keyword switch. It has one input, which is what the user types into the program. By the way, before we start, I'll show you what this application does. It asks the user to enter a day of the week, and then gives a personalized message about what day they've entered. If I run this program, please enter a day of the week. I type Monday, I dislike Monday. It's a very simple application. What I'm going to do is rewrite this as a switch statement. It takes the user's input, which we've put in a variable called input. Just like most things in C Sharp, we open and close curly braces and put all the code in the middle. Now a switch statement, for example, if statement, to check different conditions. However, with the switch statement it has cases. These represent, for example, an L if statement. Our first case can be is the input Monday. We represent this like this. Then we put the code in the middle right here. In a switch statement. These three lines here are pretty much the same as these three lines right here. It's just worded differently because input is a data type string, our case needs to be a string. If, for example input is a number, then this needs to be a number. That's how that works. A switch statement can have one or many cases. We're going to do one for each of these. Every case inside a switch statement must end with a colon and must terminate with the keyword break. And all lines end with a semicolon. Every case header ends with a colon and ends with a break. That's just how it is inside switch statements. Curly braces are optional. You can put them, you don't have to put them. You can put the break inside the curly braces. It's very flexible on how it works. I just tend to leave them out as long as all of your logic here, and you can have multiple lines of code inside a break. And the colon from the header, you're all good there. That's our first case, Monday. I dislike Mondays again for Tuesday, the next case would be Tuesday. Again, we can't have the same exact case because it's redundant. The next case would be Tuesday, and we take this line for Tuesday, et cetera. You can see a pattern emerging here. The switch statement has lots of conditions inside of it. Through the power of editing, I have rewritten all of those and l if statements into one switch statement and it will do exactly the same thing. Let me demonstrate that. Now let's just temporarily cut this logic out. Now I'm going to run the application I type in Monday. You can see I'm getting exactly the same result. This switch statement right here is exactly the same as all of these ifs and L if statements here. One thing you notice is readability. It reads a lot better. You can see it's actually a lot more minimal. You can clearly see what's going on and it looks a lot tidier than this. That's one advantage of using a switch statement. A disadvantage is the booling operators. For example, if input is Monday or Tuesday but not Wednesday, we have a complicated thing right here. These are quite difficult to achieve with switch statements and it gets a lot messy real quick. In that example, I would prefer an F statement, in that case to work with complex bolen operators. Another advantage of using switch statements is that when you actually get a lot of conditions, here we have seven, it's quite a lot. When we get to five or more, then a switch statement will actually execute a lot faster by the system. This is just due to design. What's going on in the background. When you get five cases, for example, or more, then I would prefer a switch statement over this just because it's actually executed faster. If you represent seven cases in if and else if statements, then the computer has to evaluate every single one. It goes, oh, this one, is it this one? Is it this one? But this doesn't work in switch statements. It actually gets executed a little differently. It's more performant when deciding between switch statements if and else if statements. Then it's just up to you. You have to take your example and work out which one works best for you. One thing I'm going to mention with switch statements, one last thing is, what happens if none of these cases happen? What if there's a magical eighth day of the week, or maybe the user actually spelt one of these incorrectly, Then none of these cases will actually happen. If we did this example with if and else if we would have a final L at the bottom that would read something like, it would read something like this telling the user they've entered an invalid day because maybe they spelled it wrong. For example. How do we represent this in a switch statement? Well, we use what's called the default keyword. If I type default, always end it with a break, just like the cases above, then I can put that same code right here. If I remove this logic and test the application, then purposely spell one of the days incorrectly, you can see it's telling the user, they've entered an invalid day of the week. So this is quite useful when you want some code to run where none of your cases actually evaluated true. So it's like a catchall, for example. 24. 4-8. Conditional Operators: Let's talk about conditional operators in C Sharp. Conditional operators aren't limited to C Sharp. You can actually experience them in C plus plus and other languages what a conditional operator is. It's a quick way of replacing an F and an L statement. Consider this example. Here we're asking the user if they like coffee, we're taking their input and storing it in a variable. Then if they type yes, for example, then we're just setting up a variable called message, and storing this string inside it. I knew I could count on you. Anything else? We're saying we're no longer friends and we're outputting it to the screen. If I just run the software now so you can just quickly see how that works. Yes, I knew I could count on you. Very simple. But you can see we have an if statement here and an L statement as well. It takes up four lines of code with this extra can of variable here. There's five lines in total. When you develop large pieces of software, sometimes it's nice to simplify this all onto one line. It prevents bloating, and again, it could improve readability. It does depend how can I represent this on one line of code? How do I minimize this? Well, we can use what's called the conditional operator. What I'm going to do, I'm going to rewrite all of this section here using a new concept, the conditional operator. Now it's sometimes called a ternary operator, that just means consisting of three parts. And you'll see why it's called that as well. I'm just going to write this out as a conditional operator, then I'm going to explain it afterwards. Like I said before, it consists of three parts. The first part is the condition, this is separated by the second part with a question mark there. Then the second part is if the condition evaluates to true. The third part is if the condition evaluates to false. Now, this one line of code here does exactly the same as all of this here. Let me prove that to you. If we do this, we run the program. Do you like coffee? Yes, I knew I could count on you. And let's just test the other condition. Anything else? We're no longer friends. You can see it's much more simplified now. We've put all of that on one line of code. But how does this work? What happens is we're storing the result of this into a variable called message, similar to what we're doing here. The first part of the conditional operator is the condition is the user's answer? Yes, we're testing for a string. This is the condition. The first part of the conditional operator lives between a question mark and a colon. That is, if the condition evaluates to true. If this is true, then this segment of the conditional operator is run it then this section here, if you can imagine this queslonre, meaning else's, if it's false. And this is the condition, this variable is just taking the result of this whole condition here, a conditional operator. It's just a quick way of writing an F and an L statement on one line of code. The readability, Yeah, it does depend if you can neuter conditional operators. It may look a bit confusing, but the more you can use them, it does actually condenr code down a lot. Consider if you have maybe 50 or 100 of these, it's nice to simplify on just one line of code for example. But that's how you can write lever, conditional operators in C Sharp. 25. 5. Arrays: So I'm going to introduce a new object type into our learning. And that's what's called an array. What is an array? Well, in plain English, an array is a collection of something. For example, say one of your friends has a nice collection of video games. You might say, oh, that's a nice array of video games you have. It just means a collection of something, a lot of something. In programming, it's very similar. Let's take a look at this very basic example here. What I have here is six variables of type integer. Integer is the data type. I'm just outputting the first one to the screen. Very simple. Say if we emulate a lottery application, the user picks six numbers and then we put each of their numbers in a variable and all the variables are unique. But what if the user picks 1,000 numbers? Then I'm going to have to create 1,000 variables. It's going to be really tedious. Our application is going to use more memory, it's going to be larger in file size, and it's going to take a really long time to develop as well. How we can overcome this problem of having all these variables with different unique names is use what's called an array. What the array can do is group all of this information together into one variable only. Let's take a look how we can represent six lines of code here on only one simple line using arrays. So what I'm going to do, I'm going to define and initialize an array right here. We want all our items inside the array to be integers, numbers. We're going to use the int datatype for our array here, then I'm going to use open and closed square brackets. That's telling the system, hey, I want to create an array. We're going to give the array a name. We're going to call it numbers. We've declared the array right there. And now we want to initialize the array, which means we want to put some data inside it. And we can do that on the same line. To do that we're going to say no. Then I'm going to put the data type again, the square brackets again. Now I want to put values inside this array. I use open curly braces, closed curly braces, and then a semi colon. Now inside these curley braces, I'm going to put the values, so I can put two. When I put a next value I use a and then 12, and now the next value, 264,556.71 Now this one variable here called numbers is an array of type integer. These are all the values inside it. Now this one line of code represents all of these six lines here. Now we no longer need this. Now how do we actually access the numbers inside this array? Well, we take the name of the array, which is numbers, then we use square brackets. Inside the square brackets, we put an index for our values. Now, when we talked about substrings before, I said the index is generally in C sharp. Start at zero, this is item slot zero. This is item slot number 12345, even though we have six items, this is index five because this is index zero, bear that in mind when working with arrays and collections and things like that in C Sharp. If I want to access this first item, the number two, I just put zero in there, because it's at index zero. If I run the program, now you can see it's outputting number two here, which is our first item. Similarly, if we want to access the number 12, I just put one and I can run the program, and then it outputs 12. So very simple, That's how you actually access the information in the array. You use the square brackets, but you put an index inside them. If we try and access an item outside of our array, for example index 45, well, we only have six items in our array. If we run the program, it's going to throw an error. And typically the error will say something along the lines of it's outside the bounds of the array. That's because we don't have 46 items in our array. It's just telling us unit doesn't exist. I don't know what to do. One other thing you might want to do with an array is you might want to define the array. But we don't know what information we want to put in it yet. Maybe we want to define the array here, and then we want to do some other cool stuff. And then later on, further in the application, we might finally know what numbers we want to put in here. For example, what we do in this case when we define the array here, we want to put like a capacity in here. It says here, if we actually hover over this red line, array creation must have an array size or identifier. Basically, it's saying, how many items will you have in your array when you want to use your array? I know I'm going to have six numbers because it's like a. For example, it could be a lottery application where there's only six numbers. We define it with a five here. If the index starts at zero, then we have 012345. By putting a five here, we're saying we're going to put six numbers in this array. I hope that makes sense. Now we've defined the array, now we still need to initialize it because we have no values in here by default, if I try and access the values in the array, even though there's no values in here, it's going to output zero because this is default behavior. What I want to do is now put a value in the array. So I'm going to put a value in the first slot which is index zero. And I'm going to put the number 777 in here. Now when I run the application, you can see, we can see the value 777 and that's how you actually initialize an item in your array. Similarly, if I go to the next line and try and put a value in the next one, visual studio is actually predicting what we might want to do here. You see these gray characters here. That's basically saying if you press Tab on your keyboard. So let's do that. It's going to enter that for us, which saves a lot of time when programming. Then we can put that in there, for example. Then we can access index one, which should be the value 456, which it is. That's actually how to put values in our array, because we've only defined an array that can contain six items. Similarly, if we try and put a value in slot 45, it's going to throw an error as well, because we're outside of the bounds. The last thing I'm going to talk about with rays, the first thing before, the last thing, Rays, is one of many collection types you can use in C Sharp. There's array lists, lists, dictionaries. This is something to get you started with on how to manage lots of data, for example. The last thing I'm just going to go over quickly is your arrays can have pretty much any data type. We can have an array of strings, for example. This could be people's names. Then we need to make sure when we initialize it, it actually matches the data type. Let's delete that now. We can put some names in here. We can put in Henry. We can put in our friend Bob, et cetera. Now we have an array of strings. Okay, when we access our array, we can just do it exactly like before. And there's access Henry, which is the first item there. When we run the application, you can see it outputs Henry. Remember, when you define an array with a string data type, all the values need to be strings. Similarly, if you have an integer array, you have integers here. 26. 6-1. While Loops: Now for something completely different, I'm going to introduce looping in C Sharp. To introduce looping, I'm going to introduce the wire loop. Consider this example. Here I have a number counter. As soon as we open the software, it's saying to the user, welcome to the number counter. Please enter a number, 1-3 Let's run the application. When I enter the number three, for example, it counts to the number, I input 123. If I enter the number two, then it'll count to number two. This is represented by these series of if and else if statements. If the user enters two, it just outputs 123123. It counts to the number that the user enters. However, consider if we want to modify this application and ask the user for a number 1-1 thousand, for example. Now how we would represent this with if statements for each number, we would have this whole block. If we have the number four, then we're going to add another else if statement here, put in the number four. Then add another line here where we count to number four. But if we go all the way to 1,000 then this is going to be huge. The file size of our software will be huge, it will be really slow to run. How do we solve this problem? Well, we can represent all of this logic here by using a loop. We're going to use a while loop. Let me write out the y loop format. So you can see, just like the statement, it looks quite similar. Consider the if statement, we have a condition. If the condition evaluates to true, then this line of code is executed one time. If the condition is false, it goes to the next if statement and checks this condition. If that's true, it executes this code block once. However, with a wire loop, if this condition is true, then it will keep repeating the contents here. If I put console right line is one. If this evaluates to true, then it will just keep repeating this over and over and over until this evaluates to false. That is how a wire loop works in principle. Let's take a look at our example and how we can modify our application to do all of this if logic here in one single wire loop. Let's delete all of that. What I want to do is I want this wire loop to keep looping, looping, looping, and outputting the number up to the number that we input. This is the user's number that they're going to enter. And we want the wire loop to keep looping till this number is reached. Okay, how do we do that? I'm going to introduce a new variable and I'm going to call it counter. And I'm going to initialize it to one. What counter will be? This is the number that's going to keep incrementing 123 all the way up to the number that the user gives us. What I want to do is output counter to the screen. Every time this wire loop loops, I want to output the value of counter. It starts at one and then I want to increment counter by one each time what I could do is equals itself plus one counter has the value of one, but now I want it to equal itself, which is one, and then add one to it. Now after this, counter will equal two. If it runs again, counter will equal 34, et cetera. Now, anytime you add one to a variable, you can do it this way or you can do it this way. Just like that. This plus plus adds one to the current value. That's just a shorthand way of typing this. It's exactly the same thing. It doesn't work with two, only one. If you want to decrement it by one, you use negative, negative and that will subtract one from its value. But we just want to add one. Every time this wire loop loops, it's going to output counter one, It's going to add one to it and then it's going to go back to the start, check the condition, If it's still true, it's going to execute these two lines of code. Again, that's how the wire loop works. It's going to keep looping, but now we need a condition. The condition should evaluate to true until it gets to whatever the user entered, and then it needs to escape from the wire loop and carry on with the rest of the software. What condition can we put in here to make this true? Well, we want to count to the user's number. Including the user's number. What we want to do is say while the counter. Is less than the user's number, then repeat this code. However, we want to include the user's number as well. When it finishes counting, it will be less than or equal to. Let's just run this application real quick so we can take a look at this. Now, enter a number 1-1 thousand. Let's type in number seven, for example, and press Enter. You can see here it counts all the way to seven from number one. That's essentially how a wire loop works. If we run the application again and type in 1,000 it counts all the way to 1,000 and then stops at 1,000 You can see with not much code at all, we can replicate all of those if and else if statements. In a very simple wire loop such as this one, just so we're 100% clear, the software runs, it takes the number from the user counter is initialized to one. This is now one, while one is less than or equal to whatever number the user put in here. Let's say the user typed in 44, while one is less than or equal to 44. Continue this code execution output counter to the screen, which will be one. And then increase counter by one. Now this is going to equal two. Now counter equals two. Yes, it's still less than or equal to 44 again. Now counter equals three, it's still less than 44. Keep continuing this. Once counter equals 45, well 45 is not less than or equal to 44. What happens is it breaks out of here, jumps to here, and continues with the rest of the program. That's essentially how the wire loop works in a shop. I want to talk about something very important. Now we're introducing loops. With wire loops and any other loops we'll talk about in the future. There's a real danger of loops looping forever. They're just endless loops. What happens when you get an endless loop is it will slowly eat up the memory in your system until either there's no memory left or something overflows or something catastrophic can happen. This is a real danger here. Let's take a look at a very small example. Remember with if statements, there's a condition here. If that evaluates to true, then it's going to run this code right here that may just write true in here. What happens is this is always true, is always going to evaluate to true because I've written true there, nothing is changing this in this code. Even Visual Studios grade this out because it knows it's just going to loop on this forever. This is a very basic example. Of course, this can be achieved by using variables that never reach their expected value. For example, this will just continue to run forever if I run the program. Now you can see it's just endlessly counting. And what's going to happen is either this number is going to grow too big for its container, or we're going to run out of memory on our system. But essentially this loop will just never end and something will cause this program to crash. So it could be memory, it could be anything. And usually it's something very unexpected. So this is an example of where a loop can potentially loop forever. This is quite common, and this is why we have to test software to make sure this doesn't happen, but now we're introducing loops. This is a real danger that can happen, and it's something you should be aware of moving forward. 27. 6-2. Do While Loops: I'm going to introduce a variant on the Wile loop called the Il loop. There's a very subtle difference between the Wile loop and the Il loop. The difference is that in a Il loop, the code inside the loop is executed at least once. What does that mean? Let's consider this sample application here. Welcome to the number counter. We get a number from the user, 1-1 thousand. Then from one we output in increments of one, the numbers up until the user's value. If the user enters seven, it counts to seven and then continues with the rest of the program. We can use what's called a Wile loop to achieve pretty much the same thing here. When we reach the wire loop, here we have a condition. The code executes this, this, this, then it gets to this wire loop. If this condition is false from the get go, then this code will never be executed. The whole wire loop will be skipped if this condition is false and the rest of the software will continue to run with a i loop. Now, this is not the case, that is because the condition in a loop happens once. The loop has already executed at least once. Consider this. Now, this does exactly the same thing as the other piece of code. The software executes, this line of code is run. This, we get the user's input, we initialize this variable. Now we reach this statement, well, nothing is preventing us from going in here. This is ex, this is executed this. And then we have our condition. These two lines of code have already been run before we get our condition. And the condition says, is the counter less or equal to number? Now, if this is false from the get go, I could even type false in here. Then these two lines of code they've already run, they've already executed. Even if the condition is false, these still run. And then we continue with the rest of the software. Consider this example. It doesn't matter what I put in here. Now you can see as output one at least one time. That is because these two lines of code have already run. Even though the condition was false. A wile loop is useful when you want the code in your loop to run at least one time. If you don't, then consider using a Wile loop instead. But both can achieve pretty much the same result. But that is the difference between the Wile and the Wile loop. 28. 6-3. For Loops: I'm going to introduce a different loop now called a four loop. A four loop is just another way of achieving a result. It has advantages and disadvantages depending on your application. Consider this example here, where we ask the user for a number and it just counts to that number using a Wile loop and outputs every number along our way With a low four loops are slightly different. You see this Y loop here, we defined a variable just above it, and then we increment this variable by one every single time this wile loop iterates. When the condition is false, it breaks out of it. You can see here we've added some extra stuff to the wire loop in order for the wire loop to achieve its goal. Now a four loop, it has an in built mechanism which includes a counter just like this. It's going to simplify all of this code into 14 statement. Now, what does all that mean? Let me explain. We start a four loop with the four keyword just like that. Then the header is in brackets, just like the wire loop. And then we have the curly braces. The header for a four loop, it actually has an extra little bit of information. The wire loop here we have the condition, that's the only thing we have in here. But the four loop, it actually requires the definition of the counter and the increment of the counter. The header requires three things. That's because the four loop manages our counter for it needs to know about this information, but it also needs to know the condition. And that's how we enter and exit the four loop. For example, just like a while loop, it needs three pieces of information. I'm going to use exactly the same names here, maybe with a number one afterward. I can't use variables with the same name. I'm going to copy where we initialized our counter here. I can't have the same name. I'll just put a number one after it. The next thing I need is the condition. We separate these three items using a semicolon. Then I put the condition again, I can't have the same name. Then the last one, I need the incremental, again, I can't have the same name as the wire loop above. Now, this is basically exactly the same thing as above, apart from this line here, which I'll put here. Now, this block here does exactly the same thing as all of this. Here you can see the advantage in this case of a four loop over a wire loop. That's because it keeps track of our counter fours automatically behind the scenes. Every time the four loop iterates, this counter is incremented by one every time. If we want to, we could increment it by two every time we go counter equals counter one plus two. And that'll increment the counter by two every time, for example, we could increment it by eight every time. It's really up to us what we want to do with the incremental. But typically you'll see people increment it by one every time. There are certain cases where you might want to decrease the value by one every time. It's really up to you, that's our increment. The third item, the middle item is our condition. So it's exactly the same as a wire loop in that case. The first item is where we define our counter. So we need to say, hey, we're setting up a new variable and we initialize it to one. In this case, we can initialize it to zero if we want, but we do have to initialize it. We can't leave it blank, we initialize it to one. In this case, this will do exactly the same thing as this piece of code. Here, let me just demonstrate that. Now here's our loop. We're going to enter the number seven. Why not? You can see it counts to seven. Now I'm going to remove our while loop completely and put in our broken down four loop, a lot less lines of code. I'm going to run the application, I'm going to put the number seven, and it does exactly the same thing as the wire loop. It's pretty cool, isn't it? 29. 6-4. For Loops vs While Loops: You have to ask yourself the following question. If a four loop has all this simplification, it has inbuilt, incremental here. Why don't we always use this? Why even bother with a wire loop, for example? Well, generally, four loops are used when we know how many times the loop will iterate. For example, when the user entered that number, we're counting from one, we're incrementing by one, and we're escaping the loop when the counter is less than a certain amount. This section here will output numbers 1-10 every time it increments by one. And when it's finally not less or equal to ten anymore, it's going to escape. However, with a wire loop we can do that, but wire loops are better when we don't know the number of iterations beforehand. For example, am I hungry? Let's initialize a booling variable called am I hungry, and set it to true because I'm hungry. Now when we enter the wire loop, we don't need to know how many times it's going to loop. We don't need to keep track of a counter or all of this stuff, we don't really need. The only condition we have here, for example, is am I hungry? Well, yes, true. Okay, it's true. Then inside the wow loop, we can call a method called eat food. And then we can check if we're hungry again. And then we can keep looping. Finally, once we've eaten enough food, I'm no longer hungry anymore, then I can escape out of this. But I don't know how many times this loop is going to loop until I'm full. So it's an unknown. So this is why wire loops are good for this because we don't know how many iterations it's going to happen. But we figure this out inside the loop itself. This is why wire loops are good. The number of iterations is unknown, and this is why four loops are good. When we actually know the number of iterations, we can simplify this a lot easier with a four loop. 30. 6-5. Foreach Loops: I'm going to introduce a new loop now, and it's called a four each loop. Now, the advantage of a four each loop over, say, a four loop, is that it improves readability. And it works with collections a lot easier. Now, what does all that mean? Well, let's take a look. I have a sample application here. I'm setting up an array. It's an integer array, and the array is called numbers. I'm initializing the array with all of these numbers here. All of these numbers are going to be inside this variable called numbers. I'm now using a four loop, which is going to cycle through every number in the array in turn and then output it to the screen. Let's run the application here. You can see here the application contains each of the numbers in our array. We're just cycling through our array and outputting each number along the way. We use the length property of the array to set up a condition for that. What I'm going to do now is introduce the four each loop. The first thing I said was the four each loop offers readability. Let's take a look at that now, when setting up a four each loop, we use the keyword. For each, we have the parentheses, just like a normal if statement. Four statement y loop, for example. Then we have the familiar curly braces. Let's have a look at how a four each loop looks. I'm going to do exactly the same as the four loop. So you can see it represented as a four each loop. In the head of the four each loop, I set up a variable, I say in numbers. Then for each iteration of the four each loop, I want to output the variable num. Now, what does all this mean? Well, for a start, you can see the readability is a lot better. There's a lot less code here. It looks a lot tidier, smaller, and it's less bloating. But how does it work? What happens here in a four loop? You can see we set up a variable here. Each iteration we can make use of this variable right here. This is the same in a four each loop. For every time this iterate, this variable will equal the next value in our array. The first time this runs the first iteration, num is going to equal one. The second time this loops, num will equal four. The third time nine. For example, in a four loop, this is equaling the index. Because we're just counting from zero, we're incrementing zero by one and we're terminating it when num is equal to or more than the length of the numbers in the array. However, in a four each loop, this variable here is actually equaling the values in the array, not the index. The index is 0123. But in a four each loop, Numb will equal the actual value, 14912, et cetera. We're just outputting that to the screen. You see here we're using an index in the four loop to access the number behind the index 149. But in a four loop, it actually is set as the value num is the value. We're just outputting the value to the screen. Let me prove that to you if I run the application. Now you can see it's outputting all of the numbers in the array here. The second thing I said was it works with collections a lot better. Now we've used a standard array like this integer array, but there are a lot more array types and collections in C Sharp for example, like lists and various things like that for each offers a better readability with those and it gives you more options to work with them as well. That's the benefit of a for each loop. You can see as it's a lot more readable. We don't need to define this variable here and keep track of a counter. It's a lot simple in that regard. That is, another loop in sharp, and it's the for each loop. 31. 6-6. EXERCISE - Draw a Cube: I'm going to test your knowledge now. Now we've covered some loops. And we're going to draw a cube. What does that mean? Well, for example, if the user enters the number five and we press Enter, it draws the cube. You can see there's five Asterix is across and five down. If the user enters six, then it will be six across and six down. How do we accomplish that? Let's take a look at the code here. Now, it's not doing much right now. We're asking the user to enter a number, and then we're storing their answer into a variable called num. We're not doing anything. How do we approach this problem? How do we draw these cubes? Well, we need a mechanism to keep drawing Asterixes on the screen until we reach the user's number. When something keeps doing something, we think loop in our head. We need something to keep doing something, we need something to keep looping in our head. We should think, okay, we need a loop here. I'm not sure how many loops or what kind of loop, but I know I need a loop, So that's a good start. Now, when I talked about four loops versus wire loops, I said a four loop is good when you know how many iterations it's going to do. You can use a wire loop, but I'm just saying a four loop would be better. In this case, we do know how many iterations because we have the number that the user entered, which will be the size of the cube. A four loop would be a good start to no approach this problem, let's start creating a four loop using the four key word here. Now the format of the four loop. It takes three things. We need to initialize a variable. I'm going to call it y, I'm going to initialize it to zero. Now we need our condition. I want it to keep looping until it's less than whatever the user entered. Then I just want to increment it by one each time. Now I want to output an Asterix on the screen. Let's delete that and put an Asterix in. Let's run our program and see what we have so far. Let's enter the number five. You can see we have the Asterix going down. We have five Asterix. They're all going vertically. We have it halfway there right now. But what we need to do is get the Astrixes going across as well. Every time this four loop iterates, it's drawing an Asterix and going to the next line, drawing an Asterix, going to the next line. Every iteration we need some put. Asterix is going this way as well. Every time the loop iterates, how do we get something to keep doing something? Well, that's a loop. What we could do is put a loop inside a loop. Let's take a look at that. We can't have the same variable name twice. You can see y is used by this loop. We're going to need to rename this one. Let's call this one X for no real reason. It can be whatever. It can be cheeseburger if you really want it to. Now we have two loops. We have what's called a nested loop. A loop inside a loop. Every time this loop iterates, it's doing all of this. Consider that. So let's kind of run the program now and see what we're dealing with. I enter the number five and now, wow, what is happening now? We have 25 stars going down. That's a bit wrong, isn't it? Why is it doing that? That's because every time this loop is run, it runs this loop. And every time this loop runs, we're actually writing the Asterix here, but also a new line. And now that's a problem for us. We don't want to write a new line every time this runs. Otherwise we're just going to get vertical Astrixes. What we can do, we can introduce a new method called, right. What that does, it writes everything in this string here, all of this stuff here. But it doesn't put a new line afterwards. It keeps it on the same line. That's the difference between right line which writes this and then puts a new line. However, right just writes this and it doesn't put a new line. Let's take a look at this. Now let's enter number five. Now you can see, oh, all the Asterix are going across the X axis. Now they're all going across what is going on here. Well, that's because we're not actually writing any lines at all now. It's just pretty much writing one way. I need to start putting those new lines in. Right now we have 25 Asterix is going across. I want a new line every five of these. Now we know if the user enters the number five here, This inner loop will iterate five times. Once it's done its fifth one, the code will finish this loop and continue running the rest of the code until the first loop starts all over again. Right here, I need to enter a new line. How do I enter a new line? There's lots of ways, but using the knowledge we already know, we can just do that. We're writing nothing. But then it adds that line afterwards. Let's run this. Now let's to the number six, just so we prove it's not a fluke, it's actually going to grow a bigger cube for a different number. Now we have 123456 across 123456 down. We've pretty much done it. Let's just go over this code real quick. We can take the user's number. Now we have a nested loop. The first time this loop iterates, it runs this code here, which is also another loop. Now it goes inside here and outputs an Asterix to the screen. For example, if the user enters the number five, let's replace that. It's more readable. It's going to run this five times. Now we have five Asterix on the screen. Once this loop is finished, now the loop has ended. Now we're going to print a new line on the screen. We've entered a new line, it's going to look like this. Now we're starting our loop for the second time, the main loop. Once this is started, it runs this loop again five times. Now it's going to look like this. Once the loop is finished, it prints a new line. Now it's looking like this, then it goes back to the top. That's how it works, so you can visualize what is going on here. The answer to our problem. If we want to cube and we want to draw Asterix is going down, then one loop. But if we also want them to go down and across, then consider something like a nested loop. That's how we can tackle this problem using loops in sharp. 32. 7-1. The break Statement: So I'm going to introduce a new kind of statement called the break statement. Now when we talked about switch statements here we briefly covered the break statement, but not really in any significant detail. But now I'm going to explain exactly what this does and how it works and how it can actually benefit us. Break is key. When using a switch statement, what happens is the user, for example, enters a day of the week. We store the answer into a variable. And then if they, for example, enter Wednesday, then this line of code is run here. Once this line of code is run, this break statement, it escapes out of this switch statement and the control flow of the application continues. What do I mean by control flow? Well, when we launch our software, the main method is run automatically. And then the first line of code is run, the second line, and it's sequential, it runs all the way down. That's the control flow, that's how your application is run. But the thing about the switch statement is when the control flow reaches a break keyword here, rather than executing the next line, the next one, the next one, the next one all the way down, It hits the break keyword, then it immediately skips everything after it then continues. That's the power of the break statement when used in a switch statement. Let's have a look how the break statement can be used in something like a wire loop. Let's take a look at a simple example here what we're doing, we're asking the user to enter a number. What this program does, the simple program, we're just counting up to that number. If I run the program here and the user enters the number eight, we're just counting to the number eight. Very simple. We're using a Wile loop to do this. We have a condition here. We're saying if our counter is less than or equal to the user's number output, the counter then increment the counter by one and we're just looping that. It's very simple how it works. Sometimes when creating a loop, like a wire loop for example, or even a four loop, you might not have a condition. In this case, we set up a condition because we know what the user is going to enter, and we're counting up to that. But in some cases we don't have a condition. We can't have a condition. We might not know what the end goal is and we might actually work out the end goal inside our wire loop. You know, something might be figured out at a later date. For example, if downloading a file from the Internet and we download the file in pieces at a time and we might not know the file size of the file we're downloading. So in that case, we can set up a wire loop and just keep looping forever and ever and ever until the file is downloaded. In cases like that, we don't have a condition. So what we can do here is set up a condition which is always true. What this is going to do is loop indefinitely until, for example, we've downloaded all of the file and then we can escape out of the loop manually. This can be quite common as well in the case where we don't have a condition and we just have this wire loop loop in indefinitely, what we can do is break out of this wire loop to prevent it from looping forever. This is a good way of using the break keyword. We can use it in switch statements, but we can also use it where we have an indefinite condition, which is always true. For example, let's take a look at this example. And what I'm going to do, I'm going to rewrite it using a break keyword instead, and it's going to do exactly the same thing. Let's say we don't have a condition for this wire loop. It's going to loop indefinitely. We need a way to break out of here, so we're not stuck in an endless loop. What we're going to say is if the counter at any point is greater than the number the user entered, then break out of the loop. You can see as soon as I typed that break keyword, this wire keyword also highlighted, and that's Visual Studio helping us out. For example, we could have a wire loop inside another wire loop. Inside a four loop, we can have cascading loops. And it can be quite confusing when using a keyword. Break Visual Studio is just saying, okay, you've typed the break keyword, this is the loop that it's linked to. And this is the loop you're going to break out of, just like the switch statement. For example, this break keyword will prevent this wire loop from repeating forever. It's literally saying, okay, this condition evaluates to true, let's get the hell out of this loop and continue with the rest of the program. The brake keyword is controlling the flow of execution of the code. It's basically saying, let's get out of here and continue with the rest of the program. That's what the brake keyword essentially does. Let's run the software and just confirm it does exactly the same thing. Let's enter the number eight for example. You can see it's counting to the number eight. Using the brake keyword is another way of accomplishing the goal before, but it's commonly used, for example, when you don't really have a condition and you want to escape out of a loop. That's the power of the brake statement in C sharp. 33. 7-2. The continue Statement: The continued statement, what is it? What does it do? Now I've explained the break statement. And a break statement just as a refresher breaks you out of a loop completely and continues with the rest of the program. Break statements can be used in four loops. While loops, four each loops, all kinds of loops. Just to escape out of the loop, It's not looping indefinitely. However, the continued statement, what that does is just skips one iteration of a loop. What I'm going to do, I'm going to show you how the continued statement works in a four loop. Consider this example. Here, I'm asking the user to enter a number on what I'm going to do, I'm going to count to the number ten, but I'm going to skip whatever number the user enters. Let's take a look at this example. So I'm going to enter the number six, and you can see the result here. I'm counting from zero, I'm going all the way to ten, but I'm skipping the user's number. The number six. It goes 5-76 is being skipped. I'm using a four loop to accomplish this. I'm counting 0-10 I'm using a variable called. I'm saying if the counter is not equal to the user's number, then just output the counter to the window. A little bit of trivia for you, if you've heard of the C programming language. And plus, plus, we've talked about the incrementa before, where you add one to a variable, you put plus, plus. You can see now this is how, where plus plus came about, the programming language C plus, plus, It's just one more than its predecessor. That's pretty cool, isn't it? If you've ever wondered about that. Anyway, how can we accomplish this using a continuous statement? Let's take a look at this. I'm going to rewrite this using a continuous statement. I'm going to say if the current counter is equal to the user's number, then continue. This is going to do exactly the same thing. This right here, let me prove that. Let's enter the number six. Again, you can see it's actually skipped the number six. How does this work? One thing you'll notice when typing continue or hovering over it, just like the brake statement, it's telling you which loop it's tied to. We've written continue. It's saying, okay, we're tied to this four loop here. For example, if the current counter is equal to the user's number, then continue. What continue does? It prevents the rest of the content inside the loop from executing. As soon as it's run this continue here, it's going back to the start of the four loop and continuing down. This code here is never run. Even if I have lots of code here, all of this here, if this continue statement is ever executed, all of this is ignored and the control flow goes back to the start of the loop. We continue down. Again, it's modifying the flow of execution just like the break statement does. But how the break statement breaks out of the loop completely and continues the continued statement just prevents the rest of the current iteration of the loop from executing. And then it goes back to the start and then continues looping as normal. That's the difference between the continued statement and the break statement I can show you. Now if I remove that condition completely, this four loop will just pretty much do nothing. Because this code here is unreachable. Even visual studio is graded out, telling you that this is never going to be executed because we don't have a condition here. Every iteration of this four loop, we're just hitting this continued statement. And it's just going to keep going back to the start in this tiny loop here. So that's the power of the continued statement in C sharp. 34. 8-1. Exception Handling (try, catch, finally): Now I want to talk about error handling or exception handling. They're synonymous in the world of C sharp when dealing with exceptions, these are outcomes that you don't expect. If you look at exception in the dictionary, it's a person or thing that is excluded from a general statement and more significantly it doesn't follow a rule. Take a look at this example right here. We're asking the user for two numbers. We're putting their input, which is a string, into an integer variable right here. And we're using the method to int 32. To accomplish that goal, we're taking a string, converting it to an integer. The second thing we're doing here is dividing the two numbers together and putting it into a variable called result. Now this program, it's quite flaky. There's a couple of errors that can occur if we're not careful. Errors can generally occur when we're dealing with users because users do things we just do not expect. Sometimes if I run the application, enter your first number. Now what if the user just types hello? What if they read it incorrectly and put their e mail address? Users can do anything. What if they accidentally hit Enter and don't put any number? There's lots of things a user can do to potentially break your software. These are called unexpected things if I type in a lot of letters and hit Enter. Now you can see here we have this nice little error message here. It says exception unhandled. That basically means, okay, an error has occurred, an exception has occurred. And it's unhandled, which means we're not doing anything about it. The computer cannot do anything about this error because it's trying to convert this into a number. It just cannot do it. It doesn't know what to do. So we need to tell the system how to handle this type of error. If I look at this software here, this error happens when we take the user's input, then try to convert it to a number. If I hover over this method here, which we're using this method, to 32, you can see this dialogue appears. It tells us what the method does. It tells us what the method gives us back as a return. But also there's this extra piece of information at the bottom here says exceptions. Now these are the two possible errors that can occur when using this method to 32. The first one is format exception. That's the error that we just experienced. We type in a word for example, then it's throwing what's called a format exception. That's because the format is not correct. It's expecting a number, we have some letters, the format is wrong. The other error is an overflow exception. I'm guessing that's when you enter a really large number and it can't physically fit it inside the data type which is an integer. Now 32 bit integer goes to around 2 billion. If I try and put in 5 trillion, then it would probably throw that other error, which is the overflow exception. What we can do about this is handle these types of errors. When the computer says, oh, you've given me a word, I wanted an integer, I can't convert these words to an integer. We can intercept this and say, okay, the users entered some words. Now I'm going to tell you how to handle this, this is how you tackle this problem. The second error that can occur is when dividing by zero, we take the two numbers from the user. Assuming they've entered two valid numbers, we attempt to divide them together. However, if the second number is a zero, then another error is going to occur. If I put zero, now we have another error. Now it's unhandled again because we're doing nothing about it. And this type of error is a divide by zero exception. The message we're trying to divide by zero. The computer cannot physically do that. It doesn't know how it mathematically, it cannot divide by zero. But we're not telling it how to get around this problem. That's the aim of this tutorial right Now I'm going to show you how we can handle exceptions. Now this subject goes quite in depth, but we're just going to scrape the surface here. What we use here is a keyword called tri. It's quite simple, DRY like most keywords. We have our familiar curly braces. We end a curly brace here, what Tri is doing is saying, can you try to do something for me please? Because I have a feeling an error is going to occur. We know that because when we hover over this method, there's two possible errors that can occur. Because we're asking input for the user, we know there's a sign of trouble coming. We're basically saying, please try this. That's how the tri keyword works. We're trying something. Now what happens if this fails? A try will either succeed and the program runs as normal, or an error may occur. That part the catch keyword. Again, curly braces, just like before. Now, a try cannot exist without a catch. If I remove the catch keyword here, then we'll get a red line. If I hover over that, it says expected catch. Or finally, let's put that back. Red line has gone away. It's happy in this catch section here, this code will run if an error occurs here. This is telling the system how to handle this error. Let's just say an error has occurred. Let's tell the user an error has occurred. Very generic. I think if I saw this error, I would be annoyed as a user because I have no idea what it means. It's very generic, but we can expand on that later. Let's just see if it works. Enter your first number, let's put some words or letters. Now you can see we have a generic error. Error has occurred now. Our software hasn't crashed, so that's a good thing. But it's not really telling as much information. We just get this generic message. We don't know why occurred, we don't know what went wrong. It's not very useful to us, but at least our software hasn't crashed. So that's a good sign. Now let's take a look at how we can give better feedback to the user. We don't want to tell them an error has occurred because it's not really useful information. The user cannot then go back and work out what they did wrong. What we can do here next to catch is open and close parentheses and type in exception and then give it a name. This can be anything, it could be EX, you can call it what you want. Basically it's a variable we're setting up the data type is of type exception. Just how we have a data type int, This one is exception. Now we'll cover what's called a class later on, but don't worry about that for now. But now we've defined this variable called E, which is of data type exception. We can use this to get some information about our error. What I'm going to do here is when we join strings together, we use a plus here. I'm going to say message message is a string property of this exception variable here, it's going to give us some feedback, The error message that explains the reason for the exception. Now if I run the application now and enter the first number, which is a lot of letters, now we have a bit more information, error has occurred. The input string was not in the crack format. Now, when the user reads this, they can think, oh, okay, yeah, I read the question wrong, I thought it was asking for my e mail address or something like that. So now we're providing useful information back to the user. Now, what if we want to customize? What will happen? Depending on the type of error that happened. Now remember there's a couple of problems with this application. A couple of things that can occur. Number one, the user can enter some letters and it can't convert it to an integer. We've looked at that now. The other one is we attempt to divide by zero. But what's happening here is we're just doing this one line of code. Whatever happens here, error is happening. How can we customize this? Maybe tell the user they've done something wrong. If they accidentally enter some letters, then maybe do something else. If we divide by zero, what we can do here is catch different types of exceptions. If I copy and paste this, I'm going to put it here twice, and I'll explain why soon. The first exception here that can happen is the format exception. What I can do here is catch the format exception right here. What will happen here is if a format exception occurs, any error to do with formatting, We can say to the user, I don't know. We could give them a really sarcastic message. We could say, learn to read properly because they blatantly didn't read the question. Which was to enter a number and then they enter their e mail address, for example. The other one was divide by zero, okay? So divide by zero exception and the message I might want to give the user, hey buddy, you cannot divide by zero. What you doing then if it's not possible error and it's not possible error, then this is generic one. When we had that if statement, we had, then finally we had an else at the end, similar with the switch statement, We had the case. Then at the end we had default. This is what that is aiming to do here. So if none of these errors occurred, we always have our little safety net at the bottom that just spits out a message here in the real world, you probably won't have just a message here. You would probably have the system log these errors differently and these errors differently. But this is just an example. So you can see now if I run the application, I put in a word, It's now telling me to learn how to read properly. Charming, isn't it? Now, if I enter two numbers, I try and divide by zero. Hey Bird, you can't divide by zero. So now you can see it's two different things depending on what error occurred. The last thing I want to talk about is the finally keyword. Now the finally keyword goes with a tri keyword. It's optional, you don't have to use one, But it can be quite useful. Let's take a look at how it works. Finally, we'll either go after or after all of the catches after the try. If an error occurred, all the code in this finally block will be executed, even if an error occurred. If an error didn't occur, then this will also get executed. It's quite useful maybe if you work with a database or what's called threads, and you can close out connections or finalize anything that's really what it's for. But in our small example here, we can just thank the user for using the program. For example, I'm thanking the user for using the program. Let's take a look at this real quick. If I use the software, enter something invalid, we're telling the user to learn to read properly, then saying thank you for using our program. That's pretty sarcastic, isn't it? Now, let's enter some valid numbers. Now we get an actual result. Here you can see the finally block is still getting executed. Thank you for using our program. You can see finally is run regardless of whether an error occurred or not. Like I say, it's optional, you do not need this, but it can be quite useful, that is, how to catch and handle exceptions when working with C sharp. 35. 8-2. 2D, 3D and Multidimensional Arrays: I want to introduce the concept of two dimensional arrays in C Sharp. What we've looked at so far is a standard one dimensional array. By default, an array in shop is considered one dimension. However, what if we want to simulate maybe a chess board, for example, where we have eight squares going across but eight squares also going up. Then we can refer to those squares in the chess set, like a grid system with x going across and y going up. We can simulate this using what's called a two dimensional array in shop. Let's look at this example here. We've just defined some numbers here and we're storing them into an integer array called Numb. And we're just outputting the first number in our array to the screen. If I run the application, the first number in the array is one, which is correct because this is the first number. I'm going to show you an example of a two dimensional array. Now this is our one dimensional array. I'm just going to remove some numbers. The example isn't long winded. In order to turn this one dimensional array here into a two dimensional array, I use a comma inside these square brackets here. Now that is telling C sharp, hey, I want to create a two dimensional array right now. This is how we visualize our array. It looks something like that. But what I want to do is create a two D array which is going to look like this. Because the nature of two dimensions, you have one dimension going across and one going down. And then it fills out into like some graph paper, a chessboard, something like that. This is what we want to emulate here. Now I've put in commas here, we immediately get a red line because C sharp knows we're creating a two D array. But this format is incorrect. The format for a two D array looks like this. The outer curly braces here is the container for everything. Then inside each set of curly braces is each line here. If I copy this and put that in there, copy that. Put that in there. And copy that. And put that in there. Now this initialization here of the two array pretty much looks like that. This is the same as that. That's how you should visualize this. Now, how do we actually access these numbers? Again, this format is wrong. If we hover over it, we can see here, wrong number of indices. That's because it's now expecting two. Because we've created a two array here, what we can use is just the comma system, for example, 00. Now that will actually output the first number in the first block. Here's the first block, here's the second block. Here's the third block. Again, all indexes start at zero. This is the first one represented by the first number here, zero. The second number here, This is the number of the item inside the first block, which is the first one there, which should be one. This should output number one right here if we run the application there, number one, If we change the second digit, for example, two, then 012, it should output number three as you can see there. If we increase this to two, then it should out here, because it's two across and two down, we should get number nine. There we go. That is how to access information from a two D array in C sharp. Now you may be asking the question, what about three? What about four arrays? We consider this two. Now, this example is going to get way too crazy. That's minimize it down. Now this will look like this. How about a three array? Well, yeah, very simple. Let's take each one of these and replace each number with an extra set. Now, if we hover over here, wrong number of indices expected three, let's enter a third one. Now you can see the coordinate system is in three dimensions. If I run the program now the first number in the array is one, which it is. This is the very first item. So you can see this is kind of the concept of two arrays. Three arrays. And you know, it can go on from there. And you may ask the question, well, how many dimensions can we go to? Well, the answer 32, if you're ever wondering. So we can have up to 32 dimensions in an array in shop. 36. 8-3. EXERCISE - Chess - Find the Queen Game: I'm going to do a bit of a challenge now. I'm going to test your knowledge on two dimensional arrays and also problem solving. Consider this template here, It emulates a chess board. If you're familiar with chess, then maybe you've already figured that out already. If you don't, don't worry about it. We're going to create a piece of software to find all of the queens, which is represented by a Q on this chessboard. Now, this is what the chessboard looks like. We have a castle, a rook, a bishop queen, and a king, all the pawns, some empty squares represented by zero, and the other players pieces as well. If you're not familiar with chess, what we want to do is find the cue. This is a character array represented by Shah. In a character, they all go in single quotes and you can only have one letter inside, otherwise it throws an error. What we want to do is find the cues in this two dimensional array and then output them to the window. So how do we do this? How do we find something? Here's our two D array. How do we pick out these queens? Well, what we want to do, we want to test each one. Is this a cue, Is this a que, no, etcetera, et cetera. In your head, you should be thinking, okay, a loop. We need a loop. But because there's more than one dimension, we need to check going across. We also need to check, go down, we check all of these. Go down one, check all of these down. One, check, all of these. In your head, you should be thinking, okay, we need a loop and we need two of them. We already know how many iterations we need, because we have eight going across and eight going down. You should think, okay, 24 loops. Four, because we know the number of iterations and a loop, because we have to check something over and over, Let's do 24 loops. The first loop I'm going to do is the y loop, and that will move downwards. Let's start with that. We're going to start with zero, because all indexes start at zero. This is slight 00 there, y is less. Now we want to get the length of this dimension here. How do we do that? We take the name of our two array here, period. And then we want to use the get length method. When we open parentheses on that, it asks me for a dimension, well, this is the first dimension, I'm going to put zero in here. That gets the first dimension and then semicolon and increase by one each time. That's our first loop. Now we're looping down. We also need to loop across. We're going to need another loop inside our loop that will represent the x axis here. We want to get the second dimension in there, which is represented by one. Now this is going across the first dimension down here. This is going across the second dimension across here. Now we have our two loops set up. We need to actually check each one of these values. We can do that using an if statement. That we can say the current value if is a queen. And then I'm just going to say queen found at this location. Just so this makes sense. If the item at X, which is represented by this four loop, and X obviously gets incremented by one each time that goes across, that goes in the first slot here. Then the second one is the Y and that moves down. What we're doing, we're checking each value, we're going all the way across and then down one across, down another one across. That's what the loop is doing. And each time we're checking to see if the slot is a queen. If it is, the condition is true, then we're running this line of code right here that's just saying queen found at location. And we're outputting X and Y. Let's see if this works. Let's run the application. Queen found at location 03 and Queen found at location 73. If we're right, 03, this is zero. This is all of zero right here. 0123. That's correct. The next one I believe was 701-23-4567 and then 170123. You can see it successfully found both queens on this chessboard. If you want to modify that, we can find the kings, and then we can just find a K instead, and that will find the kings on the board. That was a pretty fun challenge. If any of this is confusing, go over it again. You may not get it the first time, don't worry about that. But you will slowly understand it the more you can watch this video and understand the problem. But that's kind of like a real world example where we simulate a chess board, for example, when working with two D arrays in C Sharp. 37. 8-4. Lists: Now I'm going to introduce a new collection in C Sharp and that's called a list. Now a list is quite powerful internally, it's actually built upon a standard array, but it includes a lot more options and a lot of ways you can actually work with the information inside of the array. For example, let's talk about this example right here. We're defining an integer array in C Sharp. We're just giving it some random number values. We're using a four each loop to go through each item in the collection and outputting it to the screen. If I run the application now you can see all those numbers right there. Very simple, what I'm going to do is create a new list. I'm going to mimic this functionality. You can see the difference between an array and a list, for example. Now it's a bit of a complicated subject. Given our learning so far, I'm not going to explain everything, but I will cover some of the things to do with lists. Now, how do we create a list? Well, the data type is list. Now there's a new notation we haven't really talked about. This is called generics. Now, I'm not going to talk about too much about generics because I think it's quite a complicated subject at the moment. But what I want to do is define a list which contains integers, for example, you can see Visual Studio is trying to help me out here. It's actually hinting what I want to do. It's correct. Let's just press tab on the keyboard there. And it's written in this notation out for us. I'm just going to complete this as. So we've mimicked the functionality above. Now this line right here is exactly the same as this line right here. This is a type of collection. This is a type of collection. It's an integer array. Here, it's an integer list, and they all contain the same information. I'll prove that to you. If I loop through this list right here and output all the numbers to the screen, it does exactly the same thing. How do we define and initialize a list in C Sharp? Well, we use the list keyword with a capital L in these angular brackets. Right here, we put the data type we want to store in the list. Similarly, if we wanted a list of strings, we would do that. For example, we put the data type in these angular brackets, give it a name, and then we use an equal sign. And then we want to tell the system, Okay, now we want to initialize the list. Now we want to create the list and put some information in there. We use this new keyword, repeat the data type again. Then in these parenthesis, we can either leave them blank or we can give it a capacity just like an array. We can even pass an existing collection into it, for example. What I could do is do this. This will create a list based on my array right here. You can see how it's already starting to be quite powerful. Again, I can prove that also works by running the application and it's cycling through the numbers that we've passed into it. You can see it's quite powerful in that respect. But the thing about standard arrays in C Sharp for example, let's just work with our standard array right here. If I look at the native methods to do with an array, we can't really do much with it. We have some various methods we can use, like get the length of the arrays or the number of items in the array, but not really too much else to do with native methods. What if we want to sort this information? Maybe put the smallest number at the start and then the biggest one at the end? How do we reverse the order of these numbers? Various things like that. Well, this is one of the many benefits of using lists in shop. What we can do. Let's look at a few examples of working with lists. Here I'm defining a new list. I can define a new list and just leave it empty. And then later on in the application, when we figure out what we want to actually put into our list, we can dynamically, on the fly, add items to it. So I could add this number right here. And then another one. Maybe if we want to build an application where we collect numbers from a user, we can define the list. And then later on we can add in the user's numbers when we run the software. Now we can see that the list now contains those two numbers that we've added to it using the add method here. But not only can we add things, we can remove things as well. We can do various things natively. But one of the more powerful ones, we can actually sort the data. We can sort it in order. We can even reverse the numbers. For example, there's define a list with these numbers right here. And we'll use the sort method. And what this will do, this will take all of the integers and sort them in order. That is the only thing you need to do in order to do that if we run the software. Now you can see all of our numbers are in sequential order. That's very easy to do, only just this very short one line piece of code. Here you can do various things with the list class and it offers a more powerful way of working with your data. That's not to say necessarily a raiser useless. You can accomplish these things with a raise using extensions like link and things like that, but I won't get into that now. I don't want to complicate this tutorial too much, but I'm just presenting some of the advantages of using lists when programming in C sharp. To summarize, if you have a collection of data, whether it's integers, strings, or another data type, and you don't necessarily know the capacity, perhaps you might want to add values during the application. Maybe the user needs to add items or you want to control the data in a better way. Then maybe list is something for you. Maybe it's a data type you want to explore. But it is a powerful data type, and I do recommend you use lists with your adventures in C shop. 38. 9-1. O-O, Classes and Objects: Classes and objects in C Sharp. What is a class? What is an object? What does all this mean? Well, let me explain Now, Classes and objects in C Sharp, they support what's called the programming paradigm. What does all that mean? Programming is short for what's called object orientated programming and it's a paradigm. A paradigm is just a fancy word of saying a way of doing something like a method. If you carry on with your endeavors in programming, you may see this word a lot, so I thought I would bring it up. Now a paradigm is a style of programming. Imagine a chef in the kitchen with some raw chicken. He could roast the chicken. He could boil the chicken, he could fry the chicken. But each one of those is a paradigm, a different way of getting to the end result. So that's what a paradigm is. Now, when dealing with basic programs like building a calculator or something very simple like that, paradigms aren't really important for beginners. It's no surprise, you've probably never really used any before when software only has 2030, 40, maybe even 50 lines of code. The way of structuring your software is not really that important because it's quite small programming, the programming style is very important. When you have large pieces of software, you might have 2030, 100 people working on one piece of software. Code organization is very important. So consider this for example. If you have lots of lines of code that looks like this, how do you even maintain this? It could be 50 pages long, 1,000 pages long. We need a structure, we need some organization. And that's one of the many elements of 00 programming. Now, 00 programming, it's a very large, complicated subject that has lots of advantages and lots of benefits, but that is one of them. Now o programming, it dates back to the 1950s, 1960s, but it definitely gained popularity as far as I remember in the early 2000. That's when it really kicked off. What we've really been doing so far is what's called procedural programming, where the program starts and we kind of execute each line in order. We might have a method or two. And, you know, things are very simple. But again, in very large software applications, this is quite hard to maintain. For example, 00 programming, very big, very complicated subject. I can bore you with the whole ins and outs of it right now, but I don't think that's a good way of learning 00 programming. I think the best way of learning is to deal with some real world examples and actually go through it with working examples. So do you remember the movie Karate Kid, Where Daniel Larusso is painting the house and painting the fence and sanding the floor? And secretly, he was learning all of this karate, but not really knowing why. And then at the end, Mr. Magi said, oh, okay, now test your skills. So, for the benefits of staying engaged, that's exactly how I want to teach O programming, and I think that is a fantastic way of learning 00 programming by learning by example, then coming back in a roundabout loop right at the end. So when I talk about complicated words like instantiation, polymorphism abstraction, cohesion, coupling, all these complicated things I could discuss right now. But the problem is in reality, they're motivation killers. And for the interests of preserving motivation and keeping you engaged, I'm going to do this this way and I think that will be a fantastic way of learning this classes and objects in C Sharp. What is a class? What is an object, and how does it benefit me, and why should I even use them? So far, if you've been following some of the tutorials we've made so far, we've created some basic examples like multiply two numbers together. Where we take two numbers from a user and we multiply them together, for example. And when we take a number from a user, we can represent this as an integer data type, which is quite easy. And that's all we need to do. We don't need to know any more information about these numbers to multiply them together. Similarly, if we take the name from the user, we can store this in a simple data type which is a string, and we just store the user's name. So very easy. But how do we represent a complex data type, like a user or maybe an account like a social account, or a bank account, or even a bicycle like a real world object, or a sandwich, Or even a whole planet like planet Earth or something like that. Well, so far with our cano procedural programming style, maybe to represent a user, we might have a string that might be the user's first name, and then another string for their last name. Maybe an integer for their age, and then maybe a string for their username. If they have a user name, we could have maybe a decimal or a double for their height. The list goes on. There's so many things you can store about a user. You can see I already have five lines of code for all these variables. This can page right here, is going to fill it very fast with lots of information. Perhaps I could use these five data types here. These simple data types, string, int, and double to represent a complex object like a user. Similarly, if I have a bicycle, I might want the color of the bicycle, the brand of the bicycle, maybe the measurements, things like that. And that's how I would represent a bicycle object. But how do I put all of these into its own object? For example, rather than for every user in our application, I can just type user and we could have our own data type, like a user data type. That'd be pretty cool, wouldn't it? This is one of the benefits of using classes and objects in C Sharp. Let's have a look how we can actually create our own data type in C Sharp. What I'm going to do now is create a brand new class, basically a brand new custom data type that we can use anywhere in our software. If we go over to the right hand side here, this is the name of our project right here, programming. And it has a little C sharp icon with a square around it. So I'm going to right click this. I'm going to go to Add, and then I'm going to go to class. Once we're here, we can see classes been selected. Down here, we can give the class a name. Now you can call the class whatever you would like. But it's common practice to start it with a capital letter to do with its purpose. What is the purpose of this class? What does it do? What information does it hold? Or what is its primary function? That way, when you have a very large application with maybe 1,000 classes, you know exactly from the name, what it achieves, what it aims to do. What I'm going to do is create a custom data type called User. That is going to do is store information about a potential user who might be using our software. I'm going to call it user, then I click the ad button right here. What that does, it creates a brand new class in our project. This is our project here. We've been so far, if you've been watching our previous tutorials with the default class which is called program, and we've been working with the main method. You can see here there's a class called program and the main method sits inside it. This is a default class of a console application type. But if we go over here, now we have a brand new class called User. And now we can put some information inside this class right here. So you can see Visual Studio is hinting on what I might want to put in here. Yes, it may be a preferable way of doing this, but I'm going to talk about get and set in a future tutorial. So I'm going to do this slightly differently. What we want to do here in our new class, which is called user, is to put everything about our user. So maybe the user's first name, the user's last name, the user's age. Anything to do with a user. What I'm going to do, I'm going to define some simple variables in here. So what I'm going to do, I'm going to call it maybe first name for example, and then maybe a last name, and then maybe the age, something like that. Before each of these, I just want to put this internal keyword. Don't worry about what that means right now. We're going to cover that again in a later tutorial. But what I've done, I've defined three simple data types here, two strings and an integer. And all three of these are inside the user class. This is the new class we've just created. What does all this mean? This is our custom data type right here, Just like an integer is a data type, a string is a data type. Now, user is our own custom data type and it has all of these things inside it. Let's look an example of what this means. If we go back to our main class here with the main method, we can actually set up what's called an instance of our new class. Just like when we create a string, we might do something like this. But when we have a custom data type, like a new class, for example, the format is a little bit different. It would be our custom data type, which is the name of our class, which is user, because we've created a class with the name user. You can see now this is green and it actually has some information about our class. If I type in Bacon for example, then you can see it's black, there's a red line. That's because we don't have a class called Bacon. Now we have a class called User, It's green. And we can actually make use of this. Now we're going to give it a name just like we do here, for example, with a simple variable. I'm just going to call it US. R, short for user. Then I'm going to go equal. And visual studio is giving me a hint on what I want to do. That is exactly what I want to do. I want to create a new instance of our class called user. And I'm giving it the name USR. I can give it whatever name I want, it doesn't really matter. Now I have a brand new variable, just like a variable here of type string. I now have a new variable here called US user. If I start using my variable USR and put a dart afterwards, you can see I can actually access these variables I've just created inside our class. You can see here, last name, first name, and age. Let's set up a sample user variable. If I say user first name, we know this is a string. Let's call him, I don't know. Let's call him Bob. Why not? Let's set up a last name for our user. We'll call him Bob Smith. Then lastly, Bob Visual Studio wants me to put 30. Why not? I'm not sure why Visual Studio is indicating 30, but there you go. Now what I've done here, I've created a brand new user object right here. And then I've given it some information. These fields here. These are the exact same fields we've defined in our brand new user which is like our data type, and we've given it some values here. What I can now do is actually use this information. If I do console right line, I can actually output some of this information to the screen. Let's say, let me output the user's first name, last name, and age. Let's keep the console window open so it doesn't close on us. Now let's run the application to see what we have here. Running the application, we can see we're actually outputting all of the values for our custom data type to the screen. We're setting the values this way. We're outputting the values of our custom data type, like so to the screen. When creating classes in C Sharp, such as our custom user class right here, imagine this class being a blueprint, a specification. Everything inside our class here is to do with a user, it's not to do with a bicycle or a sandwich or something random. Everything in here is involved with creating a new user. We have the name of the user, the age of the user, everything to do with a user. Imagine this being like a blueprint for that, or like I say, a specification. The process here, what we're doing is creating an object just like when we create a simple string variable called name, for example. When dealing with custom classes and things like that, these are called objects. Now you can see where the term object orientated programming came from. Because we represent real world things like users, cars, bicycles as objects like classes, USR. Here is the object, this is the data type which is a class. This process here is called instantiation. And it's called instantiation because you're creating a new instance of a class. What we can also do is create a second instance of the same class. This is the first instance. This is the second instance. We can create 50. We could create 100 for example. What we can do here is another user and maybe he's called Darren Smith and he's 75 years old. Similarly, we can output his information to the window. As you can see there, you start to see the true power of object oriented programming. We could create thousands of these user objects and replicate thousands of users in our software if we would like. We're not limited to only having user objects. We could have account objects, lots of different things to bring our software together. What we can do with these objects here, we can pass them to methods, we can put them in arrays, we can cycle through them in loops. The limits are endless. But that is only a small sample of object orientated programming. And it starts with creating classes and new objects. So I hope this helped you get started with your object orientated journey in C shop. 39. 9-2. Constructors: I'm going to talk about constructors now in C Sharp. What is a constructor? How do they work? Well, let's check it out here we have a very simple example. We have a custom class called user. We have three variables inside the class, which is information about the user and the age of the user. Then we're just setting up a new object, which is an instance of the class. We're giving it some values, first name, last name, and age, and outputting it to the screen. Very simple piece of software. I'm going to introduce a constructor into this example. Now what a constructor does, it helps us construct our objects. Here we're creating a new instance of our class. Here is our object. What a constructor does, it gives us some help with setting up this object. Let's learn by example. I think that would be easier here. Here we're setting up a new user object. I'm just going to copy and paste this one. And we're going to create a new object, another object. Okay, here I'm creating a new user called Tony, Tony Smith and his age is 41. When I set up this user, you can see it uses four lines of code. Maybe if we want to set up 100 of these, it's not going to look very elegant, it's going to look quite bloated. This is one of the advantages of using constructors. What I can do when I create a new instance of this class, I can actually pass these values as parameters. When creating a new instance, what I can do is pass in say Tony, I can pass in Smith and then pass in the age right here. Then I can delete all of these lines of code. And then essentially this line will do exactly the same thing, these four lines here. That's one advantage of constructors is code minimalization. It's represented only on one line. But how do we set this up? Because right now we have a red line. And if I hover over that, it says user does not contain a constructor that takes three arguments. Well, let's go and add one. I'll go into the user class here, I need to set up a constructor. How do I do that? It starts with the internal keyword. Now, don't worry about what internal is right now. I'll discuss that in a later tutorial. All constructors take the name of the class. The name of the class is user. I'm going to put the name of the class there. After that, I put parentheses and then the familiar curly braces. This is a basic constructor in its minimal form. We can have more than one constructor per class if we want. What I want to do is take in these values here and initialize them into our variables here. I want to put those values right here. What I need to do, when we worked with methods, it works very similar to that. I want to pass them as essentially parameters I'm going to do first. For example, first name, last name, age. When you give your parameters name, give them meaningful names such as first name, last name, and age. And make sure they're not exactly the same as these local variables right here. Give them a slightly different casing, for example, or a different name completely. I'll discuss that in a later tutorial when I talk about this keyword. For now, our parameters are coming into our constructor here. Now I want to initialize these local variables with these values right here. It's very easy to do that. I take the local variable here, I set it as the value of the parameter. That's one done already and we'll carry on for the other two. Visual studio has helped us there nicely. Let's just review what is going on here now. The red line has gone away. If I hover over this, it's working. There's no red line. I'm passing in a string, a string and an integer into the constructor for the class. When creating our object, these values get passed in as parameters into the constructor, which is all of this. Then the value of the parameters assigned, well, initialized into our local variables here. Now, these local variables here will forever hold these values as long as this instance remains alive in our system. That's pretty cool, isn't it? Let me just run the software real quick so you can see what's going on. I'm going to comment this out, and I'll come back to that in a second. Now, let's just put that there, no problems. We run the software. Right now, you can see it says Tony Smith, age 41. It looks like it's working correctly. Let me just undo those comments and talk about one more thing. You can see something interesting. Now, there's a red line underneath this part right here. When we try to set up a new object, it's no longer working. Why is that? That's because in our class here, by default, we have no constructor. It looks like this. However, once we define a constructor with parameters like this one, we can no longer set up an instance of our class like this. There's an easy way to get around that. We define just a very basic constructor with no parameters. So now you can see this red line is gone and everything's happy. How is that working? Well, when we call this constructor here, when we create this object, we're passing in three parameters. When this line is executed by the software, the code execution jumps into here. And everything is set up here. When we create a new instance using this line right here, there's no parameters, this constructor is called. Instead, this is never run, only this section here, There's nothing going on here. Now that's the difference between the two. There's actually two constructors now inside this class. This is using the first constructor, this is using the second. And we can have 50 constructors if we want to, but that's kind of how things are going on internally inside our class. So you can see constructors have allowed us to minimize code, you know, on only one line, for example. But what else can they do? You know, what's another benefit? Well, constructors like us say can help you construct your object and it kind of does it behind the scenes. So from this file right here, we don't really need to know how this user is set up. We're just kind of passing it some information and we can kind of get it back when we want it. So all of that kind of logic is hidden away from us, which is pretty cool. Constructors can internally do some stuff we don't need to worry about behind the scenes. For example, if I call this constructor by passing in the two names in the age, I could output something to the window, for example. I could tell the user, we're setting up a new user. For example, when I run the software. Now you can see I get a little message saying, okay, please wait, I'm just setting up a new user. And then it outputs the information. Constructors, do some extra stuff, they don't need to just set up variables. They could log to a database, they could talk to a website. They could open a database connection. They can do lots of internal things behind the scenes. This is how they can help construct an object, and this is why they're called constructors. Constructors are pretty powerful elements of object orientated programming. And you can see, using this example in this tutorial, how it simplifies things. Perhaps not in the class itself but definitely working from out here. You can see how simple everything looks by just using one line of code to set up an object. And we don't need to worry about the internal things going on here. That is an example of constructors in C shop, and I hope you find it quite useful. 40. 9-3. Object Methods: Let's talk about object methods. Now, here I have a sample application. What I'm doing, I'm creating a new list here. Then I'm creating three users. They all have unique information here. For example, Tony Smith is 70 years old, Bob Holmes and Tyrone Jones. Then each of these objects here, I'm adding each one to our list. Now our list of users will contain all three of these objects. I'm using a four each loop to cycle through all of the users and in turn, output all this information to the console window. Let's just take a look at that. Now you can see this is the result we get. It's just outputting all of this object information on the screen. Now what I want to do, I want to find out which of these users have retired. Have they reached retirement age or are they a pensioner? Depending what country you live in now In the UK, I'm not sure about America, but the retirement age is, I think 66 for males. We'll just use 66 as an arbitrary number. It could be anything. Tony Smith would be retired in that case, but Bob Holmes and Tyrone Jones have a ways to go yet before they're retired. What I want to do, I want to output an extra bit of information to say is the user retired? How we would normally do this is set up maybe an if statement. And we say if the user's age, age is greater or equal to, let's just say 66 is the retirement age, Then we'd say, okay, they're retired. We'd say retired. We'll initialize it to false. If they're greater than that, I'll just say retired is true, but for example, something like that. That's how we would normally set up a case where if they're retired, we'd use a condition. And then we output that information to the screen. It would look something like that. You can see we have our nice loop here with our age, last name, and age. But when it comes to retired, we have all this information. It looks a little bloated. Maybe we can move this somewhere else. Maybe inside our class here. And then just have another one liner here. This is what we can achieve with object methods. In this case, what we want to do is put this logic here, this condition inside our class. We don't need to worry about it. We don't know how it's calculated, we don't really care. We just want a little variable here, this is retired, and we can display that information. Let's have a look how we can create an object method by moving this logic inside of our class. Just before I do that, I'm going to run the application real quick. Just so we can see the result here. You can see underneath each user it says retired is true because this age is over 66 and the rest are false just because they're not 66 or over. That's going to move this logic into what's called an object method. And we define that inside our class right here. Here's our class. Here we have our variables, here we have two constructors. What we want to do is just create a method in here, we're going to use the internal keyword again, Don't worry about what that means right now. We're just going to put it in here. When we define a method, we need a return type. It's going to be a bull lien because we want to say are they retired true or are they retired false, For example. Now the name of the method I'm going to call it is retired then. It doesn't take any parameters because we have access to the age through the class itself up here. Use at age, we're just going to create our method here and then what we want to do is return something like this. Now, Visual Studio has already hinted to what we might want to do, but let's just take this here. What we're saying here is if the user's age is more or equal to 66 retired equals true, we could also say that, which is the exact same thing, because this condition will evaluate to true or false. And then the result is stored in a bolen. Very simple, really. What I want to do is take the condition here, go to our class and we want to return this out of this method here. Just like that, because we're inside our class here. We have access to user age here. We're just going to take this and we're going to put that there. We've created a method, it has no parameters, but it has a return type of booling. We're returning true or false if the user's age right here is more than or equal to 66. Coming back here, we can remove this completely. Now what we can do is take our object here, which is user, because we're going through this on a fore loop. And then we can access a brand new method that we've just created right here called is retired. And you can see that returns a bolen. So I double click that open and close parentheses because it takes no parameters. And now you can see the code looks a lot more streamlined. We don't have that kind of condition in here. We just have four kind of nice bits of code. One getting the name, one getting the age, and one getting if they're retired. I just realized I spelt retired wrong in the method there, nobody's perfect. But you can see it looks a lot more simple now. But one of the benefits and advantages of 00 anyway, is that your logic is kind of hidden away in here. Say for example, if one member of your team, if you're working on a big team, works on this class here and you work on this class here. You don't need to worry about how is retired is calculated. You don't know, maybe you don't even care. You don't even know what the retirement age is. That's okay, because the only thing we need to call is this method right here. Then maybe our friend on our software team can, you know, deal with the intricacies of working out maybe what the retirement age is. So the principle is it's kind of hiding the information from you, it's abstracting it away. And that is one of the key points of object oriented programming abstraction. You don't need to know how this works. For example, if you own a coffee maker, you don't need to know how it's going. You know how it works inside, internally, all the electronics. The only thing you need to do is fill it up with water and press the button. So that's what I'm kind of trying to explain here. We don't need to know how this works, we just need to call the method and it gets as a true or false value. So that's one of the advantages of using object oriented programming and this is how object methods work in Sea Shop. 41. 9-4. Access Modifiers (public, private, etc): Now I'm going to talk about access modifiers in shop. Sounds a little complicated, but I'm going to break it down. So it's very simple and you're going to understand everything to do with access modifiers in shop. So what is an access modifier? Now, before we talked about the kind of job a class would have, it sort of models a real world object. In this example. Here I have a video game class. When I create a new video game, for example, it wants the video game name, its publisher, and a rating for the game. So you can see a class here represents a video game object. It's like a real world object. And when we create classes, we want everything inside the class. For example, this video game class here to just be about the video game. So we don't want to talk about anything else other than the video game in here. Maybe like what food we're eating while we play the video game. Or maybe some information about the user playing the game. Because maybe that user information could be in a user class. Or maybe the food the user is eating while playing the video game would be in a food class. This is quite important with 00 programming, you keep the classes what is called highly cohesive. And that just means everything inside the video game class is directly to do with a video game. That's the general principle. Anyway, this not only benefits code organization, but it allows different people to work on this project. For example, maybe 100 people. So you can delegate one or two people to work on, say, this class. While another person might focus on this main class right here, it has multiple benefits. But how does that tie into access modifiers and things like that? Well, consider this example here. What I'm doing, I'm constructing four video game objects here. I'm putting in some sample data, what is happening behind the scenes here when I'm constructing these four objects? I'm just setting up some variables here. The name, the publisher, and the rating. You can see the parameters are coming into the constructor, and I'm just setting the values. However, secretly inside this class, what I'm doing is generating a new unique ID for each object we're creating. What's happening here is I have a method here. It's just setting this variable up here to a unique ID. You don't need to worry about what this does, but what it does, it generates a unique ID, which is unique and there should never be a duplicate. This is an inbuilt function you can use in order to do that. And it's just setting this variable here to a unique ID. So if we create a game here using this constructor, it will always have a unique ID. From this part of the program here, we have no idea this is happening. We're just passing in three values. We didn't even know it had a unique ID. We have no idea what's going on behind the scenes. And that's the beauty of object oriented programming. We don't need to know and we don't need to care. For example, I've just created this object here called Game One. When I go in here I can re edit the publisher. I can change it to a different value. Now I've constructed it. Let's say for example, World of Warcraft Blizzard have been taken over by riot games. Then I might want to modify the publisher to riot games later in the software, for example. I can do that no problem. However, what if someone can accidentally change this ID value here? What I'm going to do is go out here, game one, and you can see this ID field here. I could change this to whatever I like. The thing is I don't want anyone to change this ID field. It's already unique. I don't want any other team member modifying this value. It could corrupt the data because the ID is unique. And anyone could just change this ID value to ham sandwich, for example. You know, that could have lots of adverse effects. One, it could break the software. Two, it could cause, you know, information loss. You know, it could have many bad effects to the software. So what I want to do, I want to keep this ID private to the class. I only want the class itself to know about this ID and manage the ID internally to this class. I don't want anyone else in the software modifying any other classes or any other parts of the software to touch this ID. Maybe they can just like look at it, but I don't want them to edit it, for example. This is where access modifiers come in handy. Now access modifiers enforce what's called encapsulation, is to make sure sensitive data like ID in this case, is hidden away from users or people, or even other pieces of software that should never have access to it. That is an example of encapsulation and why encapsulation is important when generating object oriented programs. Let's take a look how we can restrict access to certain variables or even methods using access modifiers. Let's go into our class. Let's talk about various access modifiers we can have in C Sharp. Now, the first one is what's called public. You can see here public. That just means anything defined as public, you could have a variable for instance, or you can even have a method. For example, this one down here, if I make this public. And that means when we create an object of this class, we can access it from outside of the class. We can access it from anywhere in our project. Anywhere in our solution. I've typed in game one, then a little t there, and now we can access ID. We can access the generate new ID method here. That's because these are public and we can access them from anywhere. Now the other one is what's called internal. We can have variables here, we can have internal constructors, we can have internal methods. The difference between public and internal is internal is only accessible within the current assembly or project. What does that mean? Well, come across here. So far, we've been working with one project so far. Now what we can do, we can have another project in our solution. We could have 50 projects, for example. What that means in our project. Here, our default project, only the classes inside the project can access internal things. If we're in another project, maybe this project represents the database, like the data layer or maybe the front end where all the maybe graphical things are. Then they can't access internal things because it's only internal to the current project. We'll be talking more about multiple projects later, but that's basically what the internal keyword is. Another access modifier is what's called protected. Now, we'll be talking about protected later on, so don't worry about that one for now. The last one I want to talk about is private. Now, private is very important for the example I've just given with regards to accessing the ID from outside of this class. What private does it enforces? Local variables like this one or even methods like this one only be accessible from with inside the current class. What I've done, I've changed this ID to private and I've changed this method to also private. If I go back to my main program here and put a dot after this object, you can see that the ID property, the ID variable, is missing from this list. You'll also notice that the method to generate a new ID is also missing from this list. You can see what is happening here. It's enforcing encapsulation. It's hiding sensitive information because we only want the video game class to be able to generate new ID's and you control the ID for the video game. Nobody else in this whole piece of software needs to know about ID's. It's unique to video game and it should stay unique to the video game. Therefore, these fields should be made private because only video game needs to know about this, it's private information. So consider it like that for example. However, name is publisher is public. Let's make rating internal. As long as I'm working inside the same project, I should be able to access name, publisher and rating. Which I can do right here, Name rating and publisher. Right now ID is private. If I trying to use that anyway, for example, put some information inside ID there. You can see I have an error here. And if I hover over that, it says video game dot ID is inaccessible due to its protection level. That's because it's private. We can't actually access this information if we try and run the software and compile it, it's not even going to letters. So you can see this is how strict it's enforced. As soon as I change this ID to public or internal, then the red line is going to go away. The protection has disappeared. We can run the program as normal. So this is the power of access modifiers in C Sharp. It enforces what's called encapsulation and it protects our sensitive data from either other pieces of software, other segments of the existing software, and even users working on different parts of the software as well. It enforces data integrity and prevents a lot of adverse issues that can happen because of this. These are access modifiers in C Sharp and why they're very useful when creating classes and objects. Lastly, I want to talk about what can have access modifiers. Here we have a method that has an access modifier. We have a couple of constructors here that have access modifiers and also some local variables up here. They also have access modifiers here. But you'll notice that the class that contains all of these elements also has an access modifier. Now public is the weakest access modifier. If something is made public, then anyone anywhere in the whole solution can access this item. However, the class itself is marked as internal. And that means only classes inside the existing project or assembly can access this class. By default, this stronger access modifier overrides anything weaker internal. We'll override all these public access modifiers here. And that is because the surrounding class is marked as internal. By default, the access for these will all be internal. If they're public, it will look something like that. Even if they're marked as public, this is how they will be accessed. However, if I mark the class as public, then it's no problem because this is the weakest access modifier. These will all be public if you've ever worked with file and folder permissions for operating systems and various settings can override the subfolders, It works very similarly to that. To clarify, if I was able to mark this class as private, then by default everything inside it will be private regardless of the access modifier. That's the point I'm trying to get across. Now, writing access modifiers in C sharp is optional. If I remove the access modifier from the class, then by default classes are all internal. I could write this and this would be exactly the same as doing this. It's optional, but it's assumed internal by default. However, anything inside the class, methods, constructors, properties, or variables, by default these are all private, unless explicitly marked as public or internal, Then it's assumed they're private. Writing this would be exactly the same as writing this. In this case, private is optional. We could remove the private access modifier from the method and the variable up here. And it will have exactly the same effect because by default, anything inside the class is assumed private if there's no access modifier. 42. 9-5. Properties: I'm going to be talking about properties in shop. Now, we're also going to be discussing the get keyword and the set keyword, also known as getters and setters. So what does all that mean? Well, let's take a look. If you followed along with the other tutorials so far to do with object oriented programming, then this is going to make perfect sense and lead on from that. If you haven't, then I highly recommend you watch those so you're about to understand what I'm going to show you. What is a shop property? Why should we use them? So shop properties force one of the core principles of 00 programming, which is encapsulation. And that's just ensuring sensitive information is not accessible from anywhere else. Like when we talked about this private variable here, it's only accessible inside the class and then nobody accessing it has any control over that, for example. So this is going to push that one step further. So I'm going to present a scenario here and show you one of the benefits of using a sharp properties and getters, and setters here. In this example, we've defined a video game class here. It has various variables here we can use and a constructor with three parameters. Here we're setting up four video game objects. Game 123.4 Inside the constructor we're creating a video game name, the game's publisher, and a rating for the game, let's say when our program starts, all of this data is loaded into the system. At some point later in the software the user wants to modify. For example, the name of this game right here. They've clicked the edit button, perhaps in the guy, and they want to change the name. For whatever reason, maybe the video game is now called a different name. We're going to ask the user for a new name for this game here, Game One. And they're going to type something into the system. Let's say for example, we ask them for a new name, we can set that using the variable name here. Maybe they accidentally hit G on the keyboard, then hit Enter. What we're doing here, we're just passing in their input into this variable. No problem at all. We'll go on with our day. However, maybe this is not a good idea. Maybe we want to validate this input first. Maybe we want to make sure that the game name has at least two characters or doesn't contain any numerical characters or something like that. Maybe there's some checking we need to do. This is where C sharp properties can come in. In this particular scenario, there's lots of reasons for using C sharp properties, but this is just one example we're going to go through. Now what I could do in this case is that instead of setting the name variable directly, I can create a method here called update name. And that can take in our new name from the user. What it can do, it can do various validation checks. It can say, okay, is the new name less or equal to one character? If so, then we can't update the name and we can do any other validation on the name. And then finally, we can actually update the name. For example, what I can do here is say, game one to update name. Now, rather than setting a variable, I can use a method. In order to achieve this, I pass in our potential new name which the user gives us. Then this method will either return true if it can or false if it can't. And then update the internal in a name variable here internally within the class. And that's perfectly acceptable rather than using a method in this case, because what could happen is maybe we need a method to then update the publisher, or we need then another method to update the rating. But now we're using methods to update the name, for example. Well, we can still access the name itself, so we need to restrict access to the name because we only want to update the name field using our new method, update name. So this is essentially where C sharp properties come in. And the principle of making local variables to a class private only, you can see in our class here we have all these variables right here we have three public ones and one private one. We've gone through one example and I'm going to tell you now it's common practice to make all of your variables inside classes private. That means no one outside of the class can modify these variables in any way at all. If I access the game one object. Now I can't access name directly. I can't access the publisher variable, nothing. The only way I can access or update the name is using our update method. And that's exactly what we want because when the user types in some input here, we want it to go through the validation. We want to make sure the name has at least this many letters or, you know, various other things. And then we want to finally update it. So this method here is an acceptable solution on how to do that. And it enforces that all our variables here are private because they're sensitive. We don't want other people, you know, accessing these and putting any old values in and it enforces encapsulation as well a Core 00 principle. But what if I told you there's an easier way of doing this method? We don't have to write a method like this for every single time we update a variable. Maybe there's another way. This is where C sharp properties come in. So I'm going to create a new C Sharp property. Now when we create a property, we give it an access modifier. I'm going to call it public because I want everyone to access our name field. Then the name is a string. As you can see here, name is a string, then I have to give it a name. Now, when creating properties and variables, for example, these are also known as fields. The fields themselves usually and typically are all lower case. You can see all of these are case right here. The properties themselves, they just have an upper case first letter. If the variables here have two words, then it would look something like that. Title case, for example, without the white spaces. That's common practice. The local fields here, the local variables lower case and the properties are always capitalized at the start. That's just good practice. Once we've done this, I'm going to show you a C sharp property in its basic form now. Anytime we want to update the private field name, we go through this property here, just like when I talked about the example. Anytime we want to update the name field, we use this method. Well, rather than using this method here, we're going to use this C sharp property instead. Anytime we want to access this local variable here, we're always going to use our property instead. Consider this as an accessor for our local variable here. In order to get the variable actually get the value of it, it's going to return it using the return keyword. Anytime we want to set a value, then the local variable is going to equal this special keyword here called value. That's the value being passed into this. Let's look at an example of that right now. If we go into our main class here, rather than using this method here in our example, what I want to do is say game one name. This is our shop property right here. Then we can actually give this a value like for example. Now what is happening here, we're using the property name, but internally inside this class, it's actually going in here and setting the value. This section right here inside this Get statement. This is where we want to do this validation. Let's copy all of this right here, then let's put these curly braces on a new line. Let's delete that for now. What we're doing here is anytime we set this shot property, this set statement is called. You can see here when we use an equals sign with a new value on this shop property, internally this set block, all of this is executed at the end of this, we just want to set our local variable here, name, to whatever value is passed in. That magical keyword value I was just talking about will equal this value right here, Whatever is being assigned. Any time this property here is set, which is what we're doing, we're setting it to, then we're doing all this validation here. We have to use the magical keyword value, which is the value we're actually checking. This would accomplish exactly the same as this method here. Value just replaces the name in this instance, let's just check this out and run through it one more time. We're giving the shop property name a value right here. Now, value is going to equal to, it, could be whatever. It doesn't really matter. Then the flow of execution comes in here, and this set method is called because we're setting a value, this magical keyword here. Value is going to equal because that's the value being passed in. Now we're checking that the user's, the length of the name is less than or equal to one. If it is, well we can't update it, then tough luck, We do any other validation, whatever it may be. If we can finally update it, then we're going to set our private variable name, which is this to the value which is being passed in. That is the magic of using a shop property and the set keyword here, we don't need a whole new method. In order to accomplish this, we can use inbuilt functionality. The main takeaway from this is that shop properties control access to sensitive information. And these items are all our local fields here are all considered sensitive information. We don't want users just putting any old values in here. We perhaps want some validation to make sure, you know, that the values being passed in are accurate. You know they're valid or for whatever other reason. And then when they finally are, then we can update our sensitive and precious private variables in this case. So this is the advantage of using C sharp properties. We've talked about the set keyword quite extensively. Let's just cover the get keyword real quick. The get keyword just actually gets the value of our private variable. Again, we can do various things along the way before we ultimately return it. We can do anything we want here, just like in the set keyword right here, We can do anything we want. But ultimately, we're finally going to return it out of here. What we can do here, let's output the name of the game here to the console window. When this line executes here, we're just output in game one name to the window. So you can see right here. So what happens is internally when we actually get this value, so what we want to do is get the name of the game. Internally this get block is being called. We can do anything we want here, any checks, any validation we could log to a database or a file. And then we can finally return our sensitive information here, the private field out of here, and then out to the window. You can see the get keyword, in this case controls the getting of our local variable here. Similarly, the set keyword controls initializing a value to our precious sensitive local field right here. And again, it's always good practice to have a C sharp property for every one of your private fields here. And by default, you should always make your local fields private unless there's some extenuating circumstance or special reason not to. One of the other things we can do with C sharp properties is to make them read only. What I mean by that is that the user can access the private variables, but they can't initialize them, they can't give them any value. For example, let's say the publisher field, we want to make that read only. What do I mean by that? For example, say if I want to get the publisher for any of these game objects, I would use Game one publisher. And that would be like read only I can access the information. But when I actually try and set the data, for example, setting the name, I can't do that. It won't let me, how do I go about doing that? Maybe it's a useful thing. What we can do here is create a new property for our publisher. Again, we have our familiar format, we do an upper case on the just for good practice. Then visual studio is helping us by hinting what we might want to do. That's great, I'll use them. This is how to make a property read only. We do, we just do not define a set keyword at all. Only have a get in here. Now, you can't have a set by itself, you always need a get. But you can have just a get that makes it read only. Let's have a look at that example. Now, if we want to display publisher to the screen, we can just do that. We can display the publisher to the screen. It's no problem at all, it's going to work. If I try and actually set a value in here, I want to update this publisher to anything really. You can see there's an error here, there's a red line. If I hover over that, you can see here, property or indexer cannot be assigned to, it is read only. That's just because we haven't actually set a set keyword here. There's no setter, we can't actually set a value in here. This is quite useful if you have any sensitive fields here where you only want read access. Maybe we want to read our ID field here, but we don't want the user to set it for example. Then we would have something like this where we only provide read access to our local variables right here. One other thing we can even do is add access modifiers to our and set keywords. Here we have our name here, we want everyone to get the name. But however, maybe we want to make the setting of this private. Only things inside our class here can actually do this. What we can do here, we can make the setter private. And that means if we try and set this name value here from anywhere outside this class, it's not going to letters. So if I go to the main file here, what I'm doing is trying to initialize the name as a value. I hover over that. You can see it cannot be used in this context because the set accessory is inaccessible. We can't actually set it from anywhere outside that class. As soon as I remove that, you can see the error disappears and we can set the name once again. Sharp properties are actually quite powerful, we've only just touched on them, but I think this will be enough to get you started with your endeavors in using them. What you should take away from this is that properties in C Sharp, the control access using getters and setters to your private fields, which are part of your C Sharp classes. Thank you for watching. 43. 9-6. Inheritance: Okay, inheritance in C Sharp. You may have heard the word before, you may not have heard it, but I'm going to explain it right now. So what is inheritance in C Sharp? Basically, the core principle around inheritance is to increase code reusability. And that is very important even in terms of object orientated programming, not in terms of object orientated programming. The thing is, if we copy and duplicate code, then our software will eventually be really hard to maintain. It's going to have a large file size and you're going to have a lot of trouble. Always, always reuse code where possible. Let's take a look at an example of inheritance in C Sharp. So what I have here is a very basic application. I've created a new animal object and I have an animal class for that. Let's take a look at the animal class. So here's my animal class. It has two private fields here, name and age. So the name of the animal might be Rocky, and Rocky's age might be seven, like Rocky might be a dog for example. I have two basic methods here that just echoes the name of the animal to the console window and also another method here that echoes the age of the animal. I have two shop properties here, two public properties that allow control over my private fields here, name and age. So it's a very simple class. I've created an animal object here. I've set the name property and rocky age to seven. Now I'm just using these methods here that just echo these values to the screen if we run the application. Now you can see it's very simple. My name is Rocky, I am seven years old. So that's a basic animal class there. So now let's say I want to expand my application. Maybe I want a piece of software where I can create a zoo of animals. I might want a dog class, rat class, a cat class, a hamster class. I might want maybe 20 classes and each one representing an animal in its own way. If we come over here now, we can right click the project here and we can go to add new class. And let's say we want to create a dog class. This class will have everything to do with a dog. For example, maybe zoo has hundreds of dogs and we want to manage our dogs in its very own dog class. It's perfectly reasonable. Again, we might have a cat class, a hamster class, lots of things. But what we want, our dog class, we want all of this functionality here of this animal class, because our dog will have a name, it will have an age. But maybe it has some other things, like maybe some methods to do with digging. And not all animals can dig, For example, maybe something specific to a dog. But we do want this core functionality. Our dog is going to have a name and an age. I want all this stuff and I'm going to put that in my dog class. So now I can kind of build on this. I can add some methods for, you know, the dog digging or the dog begging for treats, or maybe certain dog tricks. But the problem is we've copied all this core functionality which is going to work, no problem. But the problem is when I have another class, maybe a cat class or a guinea pig class, again, I want them to have this core functionality as well. And the problem is I'm going to have all this information in about 20 different classes and it's going to be really hard to maintain. And not only that, it's going to increase, like I say before, the file size at the application. How do we get around this problem here? Or shop has something we can utilize and that is called inheritance. Inheritance in C Sharp, it's very easy to get started, but perhaps more complex to master. But let's get started and have a look how we can do that. We don't need any of that functionality in our class. What we can do is inherit the functionality of the animal class. All of this can of stuff here, all of the public stuff anyway. And we can go to our dog class and we can use a colon and then type in the class we want to inherit the features from. In this case it's going to be animal just by doing that. One very small piece of code here. Now our dog class knows about all of the public methods here and any public properties we may have in this class. Let's take a look at an example. Right now, you can see our dog class is perfectly empty. Our animal class has all this logic. Let's create a new object for a dog and see if we can actually use some of these properties and methods right here. Let's create a new object for a dog. I'll just call him Do. We can set the name to the dog. Bingo, why not the dog's age? We can set it to three, for example. I'm just going to rename these. You can see here, there's no red lines under these properties. There's no errors using these methods. We can even run the application, no problem. And now, look, my name is Bingo. I am three years old. You can see here, the dog has inherited all of the functionality from animal, all of the public methods and properties from animal. You can see here's the dog class right here. It's totally empty. But you can see we're re using all of this code here which is really efficient and that is the point of inheritance. In this example here, we say animal is either the parent class, like how you have a parent and a child, where the child might inherit the ability to breathe, or bleed, or eat things in your DNA. This is where the terminology comes from. The animal in this case would be the parent and the dog would be the child. But some other synonyms for that would be the base class or the superclass. Dog would be the child, the derived class or the subclass. They're all synonyms, but they basically mean the same kind of thing. When considering inheritance in C Sharp, you have to consider one thing, one thought must be going in your head, and that is a is a dog, an animal is a cat. An animal is a rat, an animal. If so, then inheritance is perfect for you. And you're not misunderstanding the concept. Always consider when you're inheriting in a shop is it's an is a relationship. Inheritance is a really lengthy subject. But one other thing I'm going to explain so it's absolutely clear what I'm going to do. I'm going to define a method inside our dog class which is unique to a dog. I want that to be, maybe bark, for example. Because all dogs bark, let me create a method where the dog would bark. So you can see I've created a method here called bark. And all it does, it writes to the console window. Woof, woof. So very simple. And just like in humans, if you have a, you can inherit things when you're born, like I mentioned before. But the parent can't inherit from the child. For example, if the child has a new ability like barking for example, then the animal has no knowledge of this. Just like in a parent, child relationship, if your child has a new skill, maybe they became an artist. It doesn't mean the parent's an artist. You know, inheritance doesn't work that way. So let me show you an example of that now. So we've defined a method in the dog class called bark. If I go to our main cannon program right here, if I put a little dot after animal here, you can see animal has no knowledge of the bark method. It's not even in this list that's expected. However, if we go to the dog here and type in, do we have our method we've just created called bark? We can run the application now you can see that you can. So the dog is barking and then we're just echoing the name and the age of the dog. That is a very basic example of inheritance in a shop. 44. 9-7. Method Overriding (Polymorphism): Okay method over riding. If you haven't seen the previous tutorial on inheritance, then I highly suggest you watch that because it follows on from that what I have here. I have a basic animal class. We're giving the animal class a name and age. Now I have a dog class. And again, the dog has a name and age and also a cat class right here. And they do various things with the animal. I'm saying the name age and making a noise same for the dog and same for the cat. If I go to my animal class here, we have the usual things, the methods from the last tutorial. But also we have one more method here and it's called make noise. All that it does is echoes something to the screen that says makes random animal noises. I have a dog class that inherits from animal. It inherits all the public functionality we have defined her. And a cat class that also inherits from animal, but they do nothing. The cat and dog classes are doing nothing Right now, if we run the program, you can see here, my name is Henry. I am five years old. Makes random animal noises. And it does the same for the same for the cat. What we're doing here, we're inheriting all of this functionality. But you can see in particular we're inheriting this method here called make Noise. Now this is part of the animal class, for instance, we might not know what kind of animal we have, we just have a generic animal called Henry. However, in my dog class, well, I know that dogs bark. For example S, I would want Lassie to bar. I don't want Lassie to make random animal noises. Same with the cat class. We have Felix. I would like the cat to for example, I could easily do that by defining a new method here called bark in the dog class. Then in the cat class, I can define a method called make noise or per, or meow or something like that, which is unique to a cat. But what we can actually do is override this method here called make noise. What that means is we can inherit this noise functionality. But it's not going to do this, it's going to do something else. That's something else we can define in our child class. For example, the dog class. How do we override this method? How do we inherit this and override it? Well, in the child class here, dog, we're already inheriting the method already because we're making random animal noises. But we want the dog to bark. So how do we do that? What we have to do in the parent class, so in this case animal, we need to make the method what's called virtual. And what that is, it's a new keyword called virtual. And that just says, okay, anyone inheriting this class, you can give your own definition to this method if you want to. It's your choice. You don't have to right now. I'm not even doing that. I run the program, I'm inheriting all this functionality. Virtual is basically saying, okay, the option is there to redefine your own content. For this method, it's optional, you don't have to. That's virtual. But what we want to do, yes, we do actually want our own functionality. For example, in this child class here, do what I want to do when I call the make noise method here. I want to bark. I want the dog to bark. In order to do that, I say bark or woof, or maybe both. Why not? I've copied this method from above, but we don't put virtual here. We use a new keyword called override. And that's again a special keyword. In the base class, the parent class, we use the keyword virtual. In the child class, we use the keyword override. That is basically saying, okay, I'm inheriting this method from the parent class animal, but I want my own definition. I want to override your cano logic and put my own override always goes in the child class, in this case dog. In the base class, we have to set it to virtual. If we don't put virtual, then we can't override it. They go together like a pair in our cat class. Well, I want the cat to me now, For example there, it's as simple as if I run the application. Now you can see here my name is Henry. Now Henry is a generic animal. He's not a dog or he is not a cat. Henry makes random animal noises. However, Lassie or Less is a dog. When we call the method make noise here for the dog, then the dog is going to bark and woof. Well, the cat's not going to make random animal noises because the cat class also overrides the virtual method. Make noise and the cat is meowing. You can see that's quite a basic example of how we can reuse this method here, make noise which is defined in our parent class, but give our own definition to it. This is reusing existing code like this method here. But we don't want this functionality, We want our own. The process of defining our very own definition is an example of what's called polymorphism. What is that? It's a Greek word that means many forms or many shapes. But it's a key principle of object oriented programming. So you've been doing an example of polymorphism this whole time, maybe without realizing. But this is the key principle of 00 programming and it's very important like you've seen already. It's achieved through inheritance and reusing code. But not only that, but providing your own definition for something. So this is polymorphism. So this is an example of method overriding in C sharp. 45. 9-8. Multilevel Inheritance: Okay, multi level inheritance. If you haven't watched the previous tutorials on inheritance, I highly recommend you watch them now because it follows on from that multi level inheritance. So let's look at an example right here. Here I have an animal class, Here it is right here. It defines some basic things to do with animals, especially this method here make noise. Now, this method is virtual, which means any child classes of this base class animal can optionally define their own content for this method. Okay, we've talked about this, now we have two new classes. One called carnivore and its parent class is animal and one called herbivore. The carnivore is like meat eating and a herbivore is plant eating and a herbivore is an animal. So is it satisfies that kind of relationship. And the herbivore overrides the method of the parent class animal and defines its own functionality, which is I'm a herbivore, makes plant eating noises, and same with the carnivore. It's overriding the virtual method and defining its own code. I'm a carnivore makes meat eating noises. Okay? If we create an object which is a carnivore or a herbivore and run this method, we're going to get this result. Now, cat and dog. Now, cat is a carnivore. Dog is also a carnivore. You can see what is happening here is the dog is almost like the grandson of animal. Carnivore class sits between dog and animal. The base class here is animal, then animals, child is the carnivore, then the child of carnivore is the dog. That's an example of multi level inheritance. We have a hierarchy here. We have the grandson, the dog. The father is the carnivore. The granddad would be the animal for example. There's multi layers of inheritance here, you can perfectly do that you find in C sharp. This is just an example. You can see here dog also overrides the method make noise. It's doing bark, woof. So let's take a look at an example. Here I'm creating a new animal, that's the base class, like the granddad. I'm creating a new dog which is like the grandson and a new cat, and then I'm calling the make noise method on each of these. I don't have a carnivore object. I don't have a herbivore object. Let's run the application here. Makes random animal noises because we don't know what animal Henry is. That's what we've defined then. Dog and cat have their own definitions for make noise. Bark, wolf and O, what happens if I remove this method here from dog? What happens? Am I inheriting carnivore? Am I inheriting animal like the granddad of this? Well, I'll show you right now, it inherits the parent class, so you can see now I don't have a method called make noise in dog. When the dog makes noise, it looks at its parent class, and in this case it's carnivore. Carnivore is actually overriding make noise and giving its own definition when we run the program. This is Henry, the random animal Noise. Let's just put that in view there. This is Henry, this is the dog. Because the dog class is now not overriding this. Now it jumps to its parent, which is carnivore that does override it. Now the dog is saying, I'm a carnivore, makes meat eating noises, and the cat still has its own overridden method defined so that the cat is still meowing. But that is a very basic example of multi level inheritance in C Sharp and how we can utilize that. How many layers of inheritance can you have? How big can build this animal family tree for example? Well, there is no real set limit, but when making software, you don't want to make it absolutely ridiculous. 234 levels maybe, might be depending on the size of your application. So having ten or 50 levels of inheritance, I can't think of an example why you would ever want to do that. But the purpose of this tutorial is just to show you like this is possible and you know it's, people use it in the real world. There is one other type of inheritance and that's called multiple inheritance. That's where a class, for example, like cat, can inherit from not only, for example, animal, but maybe something else like feline or something. So two classes. Now, shop doesn't natively support this, but it can be achieved through interfaces, which we're going to discuss in a later tutorial. So there are different layouts for inheritance, but this is just an example of multi layer inheritance. So can I get you started with? I hope this tutorial helped you consider many of the possibilities with inheritance in shop. 46. 9-9. The sealed Keyword: I want to talk about the sealed keyword in shop and it looks just like this. The sealed keyword is quite useful for restricting inheritance at class level. What does that mean? Here I have an example of multi level inheritance in C shop. I have a game class which is like the mother, for example. I have video game, which is the child. And then I have Super Mario, which is the grandchild. So it looks something like this. So here's the base class game. It only has one method that says what is cool, and it's marked as virtual. So that means any child classes of this can choose to override this method if they would like to. Then underneath the base class game, I have one called video game that inherits from game and it does override that method. But instead of saying the game is cool, it's saying this video game is cool. Then I have the grandchild class in this application that's inheriting from video game. It too is overriding the what is call method. Now it says Super Mario is call. If I look at this application here where I set up three objects and just call those methods, it's just going to output the results of those methods, That is polymorphism. What I can do with the sealed keyword, I can actually restrict inheritance on a class. Video game is like the filling of this sandwich. Its parent is game, but its child is Super Mario. So for example, if I say this was a sealed class, that means no other classes can inherit from this class, so it can't have any more children. Imagine it to be like maybe a phasectomy or something like that. However you want to try and remember that now if I go to the child class, you can see now there's a problem. Super Mario cannot derive from sealed class video game because video game can't have any more children. It's sealed. It prevents inheritance at class level here, what do I mean at class level? That just means on this line right here. However, we can actually use it at method level as well. And that restricts any further inheritance on a method, not the whole class, but just a method. We cannot put this in the base class as a rule of thumb, we can never put this in the master class, the ultimate parent. What we would do, we define a method here called what is cool. We mark it as virtual. When something is marked as virtual, that means the child class can provide their own definition by overriding the method. We've done this before. Now I go to the immediate child, which is video game. I'm overriding this method, right? This is the first time we're overriding this method because it's the immediate child. This is where I can make use of the sealed keyword. You can only use sealed with override. You can't use it with virtual. It has to be at least one level lower. Now I'm restricting any further access to this method. What is cool now the poor Super Mario class, it can no longer use this method. You can see. So cannot override inherited member, what is called because it's sealed. Using the sealed keyword prevents at class level any further inheritance of the class itself. And a method level prevents any further overriding of the method, as long as the method is marked as sealed. So that's the power of the sealed keyword in C Sharp. 47. 9-10. Abstract Classes and Abstract Methods: Let's talk about abstract classes and abstract methods. What are they? Why should we use them? Let's take a look at this example here, following on from before. If you haven't seen the other tutorials, I highly recommend you watch them because they follow one from those. We have our base class here, animal, and we're just setting up an animal name Henry. We have our dog which inherits from animal, and again a cat that inherits from animal. And we're just echoing the name of the animal, the dog and the cat. Here's our animal class. It's not doing much. We have three methods. We've marked, make noise, say age, and say name. All as virtual. If the child classes want to override these, they can do. We're now overriding same name. If we get the dog's name, it's saying, oh my name is then the dog's name and then woof at the end. And same with the cat. Not much is going on. We haven't really built on it that much. We run the program, this is what you can see, for example. It's quite normal. Now imagine that you have a very large piece of software. You have ten other people working on the software, and you want a class for each animal. You're emulating a zoo, for example. You're creating a piece of software for a zoo or even a Pokemon game. And you want a class for each character or each animal. You could have one person on your team create all these classes, but in teams of maybe ten or 100 people, you're going to delegate that out. You're not going to be the only one creating these classes. In these classes here we have one that says make noise and it's barking and wooffing. We have one that says say the name and it's saying the name of the animal, for example, the dog here. And the dog woofs after echoing its name. Same with the cat. But what if our teammate Randy, for example, he's creating a hamster class. Maybe he forgets to override this method. He remembered to say the name, but maybe he forgot to make the noise when the application runs rather than overriding make noise and it's making hamster sounds. It's just going to make the default can apparent class sound here, random animal noises. So how can we tell Randy, our friend, and you forgot to override this method, make noise, your hamsters not making hamster noises. Well, we can actually enforce this in our parent class animal. What we can do in animal, we can say, okay, I'm going to draw up a contract and say any class that inherits this class has to override, say, these three methods here. Otherwise the software won't even compile. We can't even run the software that make sure that our friend Randy, for example, overrides the methods we want our friend Randy to override. We can introduce something called abstract classes. To achieve that, what abstract classes do? Imagine it as okay, if I want an abstract class and an abstract method, any class that inherits this class here has to override those methods. They have to specify a definition. If this is an abstract method belonging to an abstract class, then if Randy, our friend, creates a Hamster class, then the software won't even run. If he doesn't provide his own definition for these methods, that's the advantage of an abstract class and an abstract method. I'm going to show you how to set that up. Now the first thing we do to set up an abstract class is to mark the class as abstract. That's just as simple as writing the abstract keyword there. That does a couple of things. Once we mark a class as abstract, we can no longer create an object from this class. What does that mean? If we go to the program here, you can see we're creating an animal object here called Henry. Now we don't know what animal Henry is, he's just been used in our example. But you can see here now there's a red line underneath this new instance line right here. When I hover over that, it says, cannot create an instance of the abstract type or interface animal. That is because if you mark any class as abstract, you can no longer create an instance of that class. Now, Henry, we're going to have to decide what kind of animal Henry is at this point. He's either a dog, a hamster, a cat, or something else. But now we've marked this animal class as abstract. We cannot create an instance of animal. Henry is going to have to go and we're going to have to make a decision on what Henry is. But that is by design. If you have an abstract class, you can't create an instance of this class. Now, abstract method. So we have our abstract class set up. Now we're going to create an abstract method. Like I mentioned, if a method is abstract, then any child class inheriting this class must provide a definition. For example, our dog class do class inherits from animal. What I'm going to do, I'm going to delete these two methods. Dog is just inheriting the normal stuff. Now, I'm going to mark this method as abstract. This is an abstract method. When I mark a method as abstract, we cannot provide a definition for the method. Like I mentioned before, it enforces in all child classes to provide their own definition because we can't even create an instance of this class and we're just enforcing child classes to provide their own definition. Then there's no sense in even having a definition here because it's irrelevant. It would never get called or reached when you define an abstract method, it's just a template. It's just saying, okay, all child classes, you need to provide your own definition for this method. In the cat class, we're doing exactly that. We have our own method here and we're overriding it when you define a method as abstract in order to provide your own definition, just like virtual, you use the override keyword here. Now in the dog class, you can see there's an error. If I hover over dog here it's saying look, dog does not implement inherited abstract member animal make noise. You can see the software isn't even compiling. We simply cannot compile the software. That is the reason what we have to do, we have to define that method. Our friend Randy who forgot to his definition for his hamster making hamster noises. Well, now the software physically will not compile unless our teammate remembers to overwrite these methods. That is a very good use of having an abstract method. We can do this for all of these methods. For example, for example, say name. We can define a template for that. You may ask yourself, what's the point in even having a method? Then, for example, why even have say, age well. That's because all our child classes like cat and dog, they can still use say, age in here. For example, we can call say, age in these methods, we can use them from any child class of this. These methods are still useful. So this is a standard method, but this is an abstract method. The abstract methods, we're basically forcing all child classes of animal to implement something. To give it a definition, a function, that's what an abstract method is. It's forcing all child classes to implement a definition for them. However, we can still have normal methods like say age for example. We can still use virtual and have dog and cat override the virtual methods. Those are perfectly fine, but that is the point of abstract. So using abstract classes here, like animal, not only enforces abstraction, which we talked about with access modifiers earlier, but also polymorphism as well, where we can define our own can of function for these methods. Here, not only that, but abstract classes can enforce any child class inheriting from animal gives some functionality to these methods, consider it like a blueprint or a contract or something like that. I appreciate this tutorial might be a lot to take in, but feel free to replay it over and over until you understand. But this is the generic principle behind abstract classes and abstract methods in shop. 48. 9-11. The this Keyword: I'm going to talk about this keyword in C sharp, it looks just like this. What this is, it's basically a shortcut for an instance of a class. Here we have a class called dog, and I'm creating an instance. This can be a shortcut for this instance here. If I look at my dog class here, it has one method called make noise. When we call that method, it's just writing bark woof to the console window. If we look at that, now we're calling make noise. If I run the program, you can see it doesn't do much. If I go inside this dog class, I can refer to this current instance when this method is being called. For example, I go in here, If I type in this, I can refer to anything to do with this current instance which is being created here. Let's look at an example of that, just so I can prove it to you. I've created a class called helper. Now helper doesn't do much. It has one method called make more noise. It takes one parameter, which is a type dog, and there's the instance of the dog. This is being passed in as a parameter to this method. We're writing a line, I'm making more noise for dog name. If I go into my dog class here, I'm going to create a new instance of helper so I can use the class. Then I'm going to use help, make more noise. I want to pass in an instance of dog. What I can do is pass in the keyword this, because this represents the instance which I created right here. When we call the method on this instance. Imagine it being remembered here. Now, this represents that very instance. Imagine this being this. Now, when we call helper, we're calling the method, make more noise. This instance is being passed in. It's come a long way. Now we're just echoing the name of the dog which belongs to that current instance. If I run the program now you can see barkworfI'k. More Noise What? It's blank because we haven't given the dog a name. Let's give the dog a name. So, dog name. Let's, let's call him Rocky. Why not Now the dog has a name. Let's run it again. Now, I'm making more noise for Rocky. You can see that's the power of the keyword, this. It takes the current instance, it's basically a shortcut for it. Imagine this being a shortcut for the current instance. And we can do whatever we want with it. We can access, access properties, access any private fields, or even pass it to different methods as parameters. That is the power of this keyword in shop. Another thing we can do with this keyword in C Sharp. Here's a good example. I see people do this a lot if we have a constructor for a class like animal, and it takes in two parameters, for example, name and age. In our constructor, we want to construct our object. What we do, we set our local field name to the parameter, like this. Then we set age to the parameter as well, just like this. Now we've done that, We can actually use this keyword to differentiate this instance of name. This is the parameter from this instance of name. This is the private field. What we can do to make it more obvious is say this. Now, this name refers to this one, because this is the current instance of this class, it's going to refer to this one. Same with age. This refers to the instance which is this one right here. However, name here refers to this one because it's not in the current instance. It's being passed as a parameter. You'll see this a lot when setting up constructors, and it just differentiates the names so there's no ambiguity. It's clearly obvious what's going on. The current instance here is equal to the parameter. You'll see this quite a lot in your future endeavors. 49. 9-12. The base Keyword and base Class Constructors: The base keyword in shop. What is the base keyword? Now, you would use the base keyword when trying to access from a child class like dog. Here, this is a child class, we want to access anything in the base class, hence the base keyword. Consider it like a short cut for accessing methods, properties, and things like that. Here, for example, I have a base animal class here that has a couple private fields and some methods. For example, this method here, it's called animal method, it's public and it's part of the animal class. What I can do from the child class dog, I can come in here and say base and then I can access animal method because this is a child class in this case. Base is optional, but you can see how it works. It adds a bit of clarity. For example, what I have here, I have a method called info that just outputs to the screen some information about this current dog. If I go over here, I've created a new object here, a dog instance. I've given it a name, an age and a breed. And then I'm just outputting the info here. So when we run the program, we can see some information about the dog. What you will see a lot is just adding a bit of clarity because name and age are both defined in the base class animal here. So you can see name, age, it adds a bit of clarity. If you look at the code, you can quickly see, oh okay, these are members of the parent class to look there. However, Breed is a member of this class, so it doesn't have the base keyword, But you can see quite easily you know where these belong just by looking at that keyword. But that's not the main feature of the base class. What I want to talk about now is if you have a in the parent class, for example, animal. If I set up a constructor in animal this, you can see there's a bit of a problem with that. If I now try and run the program, it's not going to let me, if I go over to my child class, any of the child classes, this error has appeared. This little red line. If I hover over that, there's a bit of a cryptic error message here. Now, by default, constructors are not inherited because they're not really members of a class. But now I've defined a constructor in animal here. Now it's having a problem. I can't even compile my software. What we're going to do here is define a constructor in dog here. Way when I create my dog object here, I don't have to set all these properties. I can just put them in parameters here when creating our new instance. Let's have a look at how we can do that. When we create a dog object, I want to specify a name which is in the parent class, an age which is also in the parent class, and also a breed. I want these as all parameters and breed is part of the dog class, not the base class. If I go over to the dog class here, the child class, I start creating a constructor. I want to take in the name of the dog, the age of the dog, and also the breed. It looks something like that. Now there's a shortcut here. What we can do here is pass name and age to the base class. How we do that is after the constructor here, we put a colon and put the keyword base. Then open and closed parentheses in here. This pretty much calls the constructor of the base class. Our constructor here takes two parameters. Base in this case is a shortcut for the constructor of the parent class. The constructor takes in two arguments. If we go back over here, it takes in the name, it takes in the age. Now we're dealing with these two parameters here. They're being thrown up to the base class and the constructor is called. Then we just need to do something with the breed, We set that here. Now we can set up our parameters here when we're creating the new instance. Now we don't need any of that. Essentially, this is going to do exactly the same thing if I run the program. Now you can see it outputs all of the information. One more time, how does that work? We're creating a new instance of the dog class. We're calling the dog constructor, which takes in three parameters. Here's our dog constructor. Yes, it does take in three parameters. Once the constructor is called, it takes in these two parameters and throws them up to the base class. Up in the base class, you can see there's two parameters, Here it is, calling the constructor with two parameters. We only have one constructor, It has two parameters then this is called. This sets our properties here, name and age, which subsequently set our private fields through getters and setters. Once the constructor has constructed our animal object flow goes back out and then the rest of the dog constructor is called. Which just sets the local field here, breed to breed here. That's essentially how it works in the background. It's just calling the base class constructor. Write here, you may be asking why can't we just remove that? And I do base name equals name and then the age for example. No, it's not going to work because this terminology up here, the colon base is actually calling the constructor of the parent class itself. So it is required and then that error will resolve itself without that. And even if you put those bases in there, it's still going to throw this error here because the parent class's constructor is never constructed. So it doesn't actually ever create this animal object because this is the parent class. The child class dog depends on this. This is why it's required here. And that is the power of the base keyword in shop. 50. 9-13. Interfaces: Interfaces in shop. Interfaces are another way to achieve abstraction in shop. We talked a little about abstract classes before. Abstraction is a key object orientated principle, which is just the process of hiding the internal details and showing only the functionality. Let's take a look at interfaces in shop as a mini refresher. I'll just refer to this project where we made an abstract animal class here. Here's our abstract animal class. We have some private fields and public methods here and also some public properties. I have one abstract method here, because the dog class here is inheriting from the abstract class animal, it has to override this abstract method. It's forced to do that. And that's the point of abstract classes through polymorphism. We're overriding this method, make noise. And we're just outputting woof, woof for our dog class. When we create a new dog object and run the method, make noise, we just get woof, woof. In principle, that's the abstract class there. We're forced to override these abstract methods. Here, let's take a look how we can create an animal interface and also see how interfaces differ from abstract classes as well. Interfaces in shop, quite similar to abstract classes. What I'm going to do is create a brand new interface in shop. Then I'm going to show you a few differences between abstract classes and interfaces. Then our dog class here is going to use our brand new interface. It'll all become clear momentarily. If we go over to the right hand side here to our project, right click, go to Add, and then go to class. From the menu here we just choose Interface. Now we can give the interface whatever name we would like, but I want to create an animal interface. When creating interfaces, it's always good practice to use a capital I beforehand. That's because when you add interfaces, or at least you have a really large project with maybe tens or hundreds of interfaces, you can distinguish them from normal classes. Here we have animals and you can see animals. This one's clearly an interface, just because we've named it that way. It's just good practice. The difference between an interface like this one here and a class, this one here. Here's just the difference in the keyword, which is we have a class keyword for a class and the interface keyword for an interface. Pretty much anything else right here is the same. That's the only subtle difference here. Now interfaces in C sharp, you can consider them as pretty much 100% totally abstract. What does that mean? Well, if you've watched the abstract class tutorial like this one here, we have some abstract methods here. When we have an abstract method, we don't define a body for it. Because our classes that inherit this abstract class, they define their own methods for them, like the dog class and the cat class for example. They provide code. When we go to our abstract class, it has no body for example. However, an abstract class can define its own methods like say name, say age. They can do various other things as well. This is not true with interfaces. Consider an interface as a purely abstract class where you don't define bodies. There is a little exception for that rule to do with private members, but I'm going to discuss that perhaps later or at another time. Consider interfaces as like a purely abstract class. We're not defining bodies in interfaces for our methods. If I come over to my dog class right here, which is inheriting from this abstract animal class, you can see I'm overriding a make noise method and then giving it my own functionality. I want to do the same kind of thing in my interface. In my interface, I want to define a method called make noise, which is going to be abstract because that's the purpose of the interface. If I define a new method called make noise like you say, because it's abstract, I don't have a body here. And by default this is public. The access modifier is public by default. And this is just by design of interfaces because we want everyone to use these interfaces. So just like that, we've defined our very first method in our interface. Very simple, isn't it? Because it's public and abstract by default. We don't need any access modifiers like public. It's optional and we don't need the abstract keyword. For example, this is how to define a public abstract method in C Sharp for an interface. Now I go over to my dog class. Right now it's inheriting from this abstract class and I'm all right here. I want to implement the interface. So I'm just going to put an I in front. So it now uses our interface instead of our abstract class. Now, how do we can rewrite this to make it work with our interface here? Well, when we inherit from an abstract class and we have an abstract method, just like we talked about before, we use the override keyword here. But with interfaces we don't use the override keyword, it's not needed at all. This is perfectly sufficient. For example, one other thing. If we choose not to define a method for our interface and just leave it like that. If we hover over this here, it's saying dog does not implement interface member make noise just like abstract classes. It's forcing us to provide an implementation for that method so it can force us to do that. When you have large teams of people for example, it's quite handy because then all your classes are somewhat standardized. And then you all will override this make noise method here, just like we talked about before in abstract classes. Now I have this dog class here. It's implementing the make noise method which we defined in our interface and through polymorphism, it's defining its own functionality. If I go over to the program here where we create a brand new dog object and we're calling the make noise method which is available through the interface, we're going to get exactly the same result. So let me just go over some similarities and also some differences between abstract classes in C shop and also interfaces as well. Because perhaps on the surface, they achieve a very similar thing before when we try to create an instance of an abstract class. It wouldn't let us. It's not possible, and this is through design. Even if I try and do the same thing with an interface for example, it's not going to let me even Visual studio isn't offering an autocomplete feature for this. When I hover over this new instance attempt here, it's saying it can't create an instance of the abstract type interface animal. So it's not possible. In an abstract class, we can have a constructor, but it's only called by the child classes, not anywhere outside of that inheritance chain with interfaces. You cannot have a constructor because you would never under any circumstances construct an interface. The interface just acts like a contract, so anything implementing the interface can override those methods that are available. No constructors in interfaces. If we want to do that, then the purpose is we have a class and then we implement an interface, or we inherit from an abstract class and then define our own overrides for these abstract methods. For example, this is why we don't create new instances of abstract classes and interfaces, and therefore we don't need a constructor. Something else we also touched on was the fact that abstract classes can have fields right here, which you cannot have in an interface. Again, in methods here we can define bodies in abstract classes. However, in interfaces we can't because it's purely abstract. These are some differences here. You may be asking yourself the following question. Why should I even use an interface when in an abstract class, for example, I can use fields, I can define method bodies if I want to. Why should I use an interface? What's the point? It seems more limited, yes. Maybe it's 100% abstract, for example, but why should I use one? Well, interfaces support the idea of multiple inheritance in C Sharp for example. If I have an animal interface like animal, I can create an interface called maybe carnivore for example. Then our dog class can actually implement from animal and iconivorre or maybe something else like herbivore. So it can implement from multiple classes up here, multiple interfaces, and you cannot do that with abstract classes. So this is one of the main strengths of interfaces in C Sharp. So let's take a look at an example right now. If I come over here, I'll right click the project, go to Add class interface. I'm just going to create iconivorre because the dogs a carnivore. It's also an animal. Maybe there's a better way of representing this, but let's just go through this example. So you can see the point of this. In carnivore, I'm just going to define a method called maybe eat meat because all carnivores eat meat. Just like that. Again, it's abstract and public by default. That's all we need in this case. Now if I want to inherit or implement from multiple interfaces, I separate the class from the colon, just like before. And then put in the class or interface I want to implement or inherit from. But if I want to inherit from multiple interfaces, I just put a comma here. Then I can put the next interface iconivor, for example. Now you can see there's a red line because it does not implement our new member eat meat, which is true. We haven't defined a method to do that. If I go to here and type in eat meat, now I'm implementing that method here from iconivor. I'm implementing this method from animal now. Everyone's happy, there's no red lines, everything satisfied. I can then put my own definition, something like eat meat. Then if I come over to my application here, I just type eat meat for example. Now this is the method that we're implementing from our brand new interface icon. Or eat meat. Oh, let's get rid of that because we can't create a new instance of an interface. Now I'm creating a new dog object and I'm now eating some meat. And that's a member of our new interface. You can see here, this is a very quick example of multiple inheritance in C Sharp. And it's achieved through using interfaces, which is something you cannot do with abstract classes. These are the benefits of both. You can see that through using interfaces in C Sharp and also abstract classes, we can achieve abstraction, which is a key object oriented programming principle. Now testing your knowledge of inheritance or maybe just querying that you fully understand this subject. For example, if I go over to my main application here, I can create a new method here. For example, I'm going to call it make noise. It's not going to return a value, it's just going to make some noise about our animals to the console window. And it's going to take one parameter here because dog implements our interface animal because we know through talking about inheritance before a dog satisfier is a relationship, a dog is an animal. Similarly, our cat class. A cat is an animal, a hamster is an animal. Then we can just go over to here and take in animal as a parameter because our dog implements this interface here. Then we can do things from here. We can say make noise. What we can do here, we can create a dog object. Then we can pass our dog to this method right here called make noise. Then, because the dog is an animal, then this is going to work, no problem. It's going to call the make noise method on the object here, which is an animal. It is an animal. If I create a cat object, I can use this same method because cat would implement animal. In this case, I could create a Dolphin class as long as it implements animal. Again, I can call this method, no problem. You can see this is the power of inheritance, but also using things like interfaces. This also works with abstract classes too, just like before, no problem. As long as my dog class inherits from the abstract class animal. You can see now if I run this program, you can see it's now saying woof, woof. Similarly, if I have a cat class like this one here, it implements from animal the make noise method and overrides its own kind of logic here, which is O. Then I go to the program, I create a new cat object, then I want to make noise with the cat. And as long as it's implementing our interface, then it's going to work, no problem. You can see the power of inheritance and why we use interfaces. We just have to pass the interface around the software, for example, as a method parameter or even a return from a method, or pretty much anything. Again, if I run the program, you can see through polymorphism, we're overriding the make noise method for dog and cat, but also using interfaces to pass that object around the program. You can see it's quite powerful and the possibilities are also endless. You can see here if I change this interface to our abstract class here, go to class and make sure it implements the abstract class. With abstract classes, we use the override key word because that's the difference between those and interfaces. We reflect that also in the dog class. And then go back to our main program here. Then run the program. You can see we've passed around an abstract class and it works exactly the same as an interface. But there are subtle differences, like we've discussed previously, between interfaces and abstract classes. But this is an example of both how they compare and also the advantages of using interfaces to satisfy multiple inheritance in C Sharp. I hope this tutorial helped you, and thank you for watching. 51. 9-14. O-O Summary: So we've just completed quite a few tutorials on object orientated programming. Now we've gone through pretty much every principle of the programming paradigm. And now we're just going to kind of come full circle and reflect on what we've learned, and drop some keywords and things like that. So again, like I mentioned at the start of our 00 journey, C sharp is an object oriented programming language. And using 00 will really help you structure your projects. When your projects get very large, they're going to be a lot easier to maintain. You're going to practice a lot of code reusability perhaps in the future. If you continue this journey, you're going to work with other people. Perhaps in a company that also understand programming. You're all going to know and already understand the same techniques for writing software. So you're going to hit the ground running really quickly. So let's just go through some of the terminology again just so you fully understand. And then we're going to move on to something a bit different. Object oriented programming. Again, it's a paradigm, which is a way of doing something. We talked about classes. Now classes model real world objects. So if you have a piece of software about a library, then a class might be a book. Because a book is a real world object, your book class should be highly cohesive. That means the class about the book should only be about the book. It shouldn't be about the user reading the book. So when you have a book class, all the methods, all the properties should always be about the book. This is very good practice and your classes should be loosely coupled. That means your book class should be about the book. Your user class should be about the user. And they shouldn't really have much in common with each other objects. Now objects is creating a new instance of a class. A class is kind of like the template with all the methods and properties. And when we want to create a new instance of that, you can have one or thousands if you want. That is called creating an object. So an object is just an instance of a class, and when you create an instance, it's called instantiation. Now, inheritance, inheritance promotes reusing code, and when you reuse code, it makes it more maintainable. We don't have to copy code and put it in every single class, because if we have a class like dog, then it can inherit from animal. If we have a class called cat, again it can inherit from animal. And a lot of these classes will have the same features. So you're going to use and write a lot less code. And when you write a lot less code, that means your code will be a lot more maintainable, a lot easier to manage. Not only that, the file size of the software will be minimal. And also testing the software as well, you can have a lot less code to test. So inheritance all in all is a very good principle to practice. We talked about polymorphism, that weird Greek word that means many shapes or many forms, which we achieved with method overloading. When talking about methods, how we can have different parameters but with the same method name. But also more recently we talked about polymorphism with method overriding In a base class like animal, we can say make noise. Then when we inherit from that class, in a dog, cat, hamster class, we can override that method and provide our own functionality. We can see the result of that when we run the application, like when using the, the dog will bark when using the make noise method. When using the cat class, the cat will meow. We can reuse this same method but providing different functionality. That is polymorphism. Last two. Now the last two people get confused between the two because they're very similar and they do go hand in hand. And that is encapsulation abstraction. Now, encapsulation hides the internal functionality of an object. It only allows access through a public set of functions. For example, when we talked about access modifiers public and private, because we want to hide our sensitive information, like our private fields, for example. But only access them through public methods so that way we can verify the data and make sure people aren't breaking things. Things like that for example. And also sea shop properties. When talking about abstraction, it means displaying only essential information and hiding the nitty gritty details. And we did this through abstract classes and also interfaces. So imagine like a coffee maker, if you want to brew a coffee, you press the coffee brew button. If you want to start a car, you turn the key. You don't need to know how a starter in a car works, or an alternator or battery charging. As a user, as a developer, you just need to turn the key to make the car work. Similar with a coffee maker, you brew a coffee, you don't need to know how the electronics work, how the water is heated. All of that is abstracted away from you, it's unnecessary information. If you're just an end user of these things, like a coffee maker or the driver of a car, you just do not need to know this. And that's abstraction. And we see this in everyday life, every day, multiple times a day. And that is the difference between encapsulation and abstraction. Again, both key object oriented programming terms, but they do go hand in hand a lot. And at times, it can often feel like there's a bit of a blurry line between encampsulation and abstraction for that reason. So congratulations, we've gone through all of the principles of object orientated programming. And if you choose to take up another language like C plus Plus or Java, you can take these principles across and hit the ground running almost immediately. It is not tied to C. Sharp is something very popular and also used across many programming languages. 52. 10-1. EXERCISE - Drawing Pyramids: Today we're going to be drawing pyramids and we're going to be drawing them in our console application type. And we're going to let the user decide how big they want their pyramid to be. For example, if the user types in 45, then a pyramid is going to be generated here. And it's going to be 45 lines high, as you can see right here. It looks pretty cool, doesn't it? However, if the user enters the number five, for example, then their pyramid is only going to be five lines high. This is a bit of an exercise. It's not only going to test your C sharp programming skills, but it's also going to test your logical ability. How you can look at a problem and develop a solution by breaking it down into little subgroups and then attacking the problem. So I'm going to solve this issue and I'm going to show you how I would approach this task so that you can see how my mind works and how I approach this particular problem. It's quite common to see exercises like this when conducting a job interview. For example, the interviewer might ask you how you develop a small bit of software to generate a shape or a pyramid or something like that. Because anyone can look up syntax and code on the internet. But what a lot of employers like to do these days is to test how your mind works, like logical thinking. See if you can come up with a solution on the spot and also perhaps under pressure. So I'm going to develop a solution for this and I'm going to show you how I think about this step by step so that you can see how my mind works and how I approach this problem. Let's get going. The first step is to analyze the problem. When the user enters a number, this denotes the height of the pyramid. Not only the height of the pyramid, but the number of lines that are drawn. You can see there's five lines here. The pyramid terminates when there's one pound symbol, and the base of the pyramid covers the whole line here. But you can see here, it's the height of the pyramid, which is denoted by this number. The pyramid is five lines high, that's one thing to note. The second thing to note is that all of these squares are populated. If they're not populated by hashes here, the pound symbol representing the pyramid. Then they're populated by the background, which are denoted by hyphens. Here you can see the top of the pyramid has one pound symbol, and then on both sides it has four hyphens. The next line, you can see the pyramid increases by two instead of one. Here it's now three, and then there's one less hyphen on each side. Again, below the pyramid grows by two per line, and then the hyphen shrink by one. We have a couple of rules here. Each new line, the pyramid grows by two. And each new line, the hyphen, shrink by one on each side. One last thing to note is that in this example where I have a pyramid height of five, we have nine characters along the width here, five down and nine wide. We have a lot of data to work with. Let's see how we can develop a solution for this example. If you followed our tutorials previously, you may have seen the example we did when we drew a cube on the screen. Now this exercise is a little different, it's a little more complex, but the principles and procedures behind the scenes are quite similar. In that example, we use some loops, we use four loops. This example should be no different When we see repeating data like this and like this in our head, we should be thinking, okay, a loop must be involved. Something must be looping around and iterating to generate these hyphens here. Then we need another loop to then generate these pound symbols. And then maybe a third loop here to carry on with the hyphens. There are a few ways we can approach this problem. Maybe we could have one loop where we just switch the character for the pyramid part. Yes, that may also work. When developing solutions like this. There are quite a few solutions to the problem, but the choice is yours. When you make that choice, you want to make the easiest, most time efficient one. But also generate the code which is more maintainable, more maintainable by yourself in the future, but more maintainable by any teammates which actually take on your code and develop it in the future. There's lots of things to think about. I think the way I would approach this problem is to have a main loop going down the y axis. We have a main loop which generates each line in turn. Then inside that loop, I will have one loop that generates these hyphens. A second loop that generates the pyramid part, which is this. And then a third loop which continues with these hyphens, one main loop which does the y axis. Then inside that loop, I think three separate loops. That's a perfect solution for approaching this problem. Let's take a look at that now and see if we can develop something like that. So here's the code we have so far, it's not really doing anything at all, It's just outputting some messages to the user, welcoming them to the software. Thank you for using the app. This is what it does. And then we're asking the user the question. We're taking the user's input, converting it to an integer, and storing it into an integer variable. Now what I want to do, I'm going to create a method. Because when I create a method, I can call it multiple times from multiple places, and then I can generate pyramids from wherever I want. I think all the logic for generating the pyramid of the custom size here should belong in a method. And then it's easily reusable by anything else. I'm going to create a method template. Now the method won't have a return type because I just want the method to draw the pyramid. It's going to create one parameter and that's just going to be the size of the pyramid. There's our basic method there. The first thing I said I was going to do was generate a loop, which would print each line in turn, and that would go down the y axis. I'm going to create a loop to do that. So this loop here represents the height of the canvas. So the height of the pyramid in this case, because the pyramid touches the top of the canvas that we're drawing on and also the bottom, it's safe to say that whatever number the user gives the full height of the pyramid, We have no background above the pyramid and no background below the pyramid. Doing the y axis from one less than or equal to the size of the pyramid and incrementing by one will ensure that we draw the pyramid along the y axis going down. Now inside this loop, I mentioned that a possible solution was to have three separate loops. The first one to draw the hyphens on the left hand side, the second one to draw the pyramid, and the third one to continue with the hyphens on the right hand side. Let me set up those loops now without really thinking about writing code. For example, I already have this nice template. I've just generated this template from just logically thinking about the problem. I need some loop to draw downwards for the size of the pyramid. Then inside on each line, I need something generating the pyramid and the background on each separate line. Already, I have a nice little template here without really thinking about the problem too much. When we draw the hyphens on the left, the only thing we want to do is output a hyphen to the screen. Let's do that now. Similarly, when we draw the hyphens on the right, we're going to draw a hyphen. Similarly, when we draw the pyramid, we need the pound symbol. Pretty much the only thing we need to do now is work out when these loops terminate. When we looked at the example before and the user entered number five for example, then the pyramid had a width of nine, but a height of five. The very first line of the pyramid had one pound symbol, but it had four hyphens on each side. We need to work out when to stop drawing hyphens. To work out when to stop drawing hyphens on the left hand side, we need to work out when to terminate this fore loop. Similarly, how wide we should draw the pyramid on each side and also when to stop drawing hyphens on the right hand side. And when developing software like this, some days you'll have ultimate clarity. This will be easy for you, you just type in the values. You know, you're having a good day. But sometimes if I'm just tired or I'm not in the right mindset or perhaps you're a beginner and you know you're kind of working through it in your head. Well then it's no shame using something like Microsoftic cell or a note pad just to plot all your figures so then you can use your spare brain space to work out a solution for the problem or perhaps anything else. So there's no shame making nodes or anything like that, it's perfectly normal. Let me open Excel and plot some of these figures here. I've opened up Microsoftic Cell here and I've mapped the solution here. Well, unexpected solution. Anyway, if the user enters the number five for example, then we know our pyramid is going to be five units high. When the user enters five, it's going to generate a pyramid that looks just something like this. The solution we've developed so far. I have a loop which prints each line in turn. That's our main loop. We denoted that with y. You can see here I just called it the variable y, y equals one. And it goes all the way to the size of the pyramid. Less than or equal to what I'm going to do. I'm going to put the variable y right here. The next thing inside this loop, I have three loops. One will generate this content, the next loop will generate this content, and the third loop will generate this content. I'm also going to put that over here. This is going to be the first set of hyphens one. This will be the pyramid, And this is the second set of hyphens. Now when y is one, this is the first time our loop loops. We want to generate four hyphens on the left, we want to generate one character for the pyramid, and also four hyphens on the right when y is two. Now our loop is repeating for the second time we're generating this line. Our first loop will generate three hyphens. Our second loop will generate three segments for the pyramid. Again, the hyphens are going to be the same on the right, then three and then the third line. You can see where this is going two, the pyramid will be five and the hyphens two, then line number four and line number five. I'm just going to fill out. Now you can see here's some figures on how many characters will be printed for each iteration of the loop. Now using this, you can work out what you need to do. You have more clarity in your head. You don't need to remember these numbers. You can denote your brain power to thinking about a solution to the problem. Let's look at generating a solution to this problem. When the user enters number five, then five is the size of our pyramid. Our variable size, which comes into our method, will be five the first time the loop is run. Remember y is our loop. The first time the loop is run, y is equal to one. We can see that when y is one, the number of hyphens on each side here is one less than the size of the pyramid. The second time the loop is run, you can see the hyphens on each side is two less than the size of the pyramid. You can see a bit of a rule here. You can see that when the size is five and we subtract one from the size, we get the number of hyphens on each side. When Y is 25, take away two is 35, take away three is two. You can see to generate the number of hyphens on each side, we take the size of the pyramid in this example is five and subtract y from that. That will give us the number of hyphens on each side. Let's look at generating those hyphen loops. These are the two loops that generate the hyphens on the left here and also on the right. We said that the number of hyphens for each line is the total size of the pyramid. And we subtract y from that. We just say size minus Y. To add clarity, we put brackets around there, then it adds more readability. I'm pretty confident. Now for each line, we're outputting the correct number of hyphens on the left and also on the right. What a lot of developers tend to do is run the application early. There's a couple reasons for doing that. One, you can see if your last change was correct. And two, you can just look at the current state of the application. If anything, it gives you a bit more enjoyment to see what you've done already. Let's take a look. Now, we're actually calling the method, now We're taking the user's number. We're calling the method, and then this method is getting executed. Let's take a look at the results so far. If I type in the number five, now you can see everything is on one line. So why is that? That's because after all of these three loops, we're not actually outputting a brand new line. There's a bit of a problem here also. Every time we output a character, we're outputting a brand new line two. That's also a mistake. Every time we output a character, we don't want to write a new line, we just want to write that character. So we use console to do that when we actually want a new line. Well then we're going to do that after all of these loops. Let's take a look at the application now and see what it looks like. So you can see now we have a bit of a rumbus shape. It looks quite interesting, but you can see that the number of hyphens is correct. We start with 43210. Now we need to fix this middle section here, which is the pyramid. Let's take a look at how to do that. I'm going to go back into Excel, I'm back in Excel. Now what I want to do is find out how to generate these numbers using our information available. We have the size of the pyramid and we also have the value of y. On each iteration of the loop, we've already done the hyphen amounts for each line. It look quite simple to do, but how do we generate this number using the information we have on line one? Here, the pyramid is one character, you can see there on line two, the pyramid is three. You can see on each new line, the pyramid increases by two pound symbols, 13579, they're all odd numbers here. How can we generate these numbers using the information we have here? For those of you that are good at mathematics, it's probably quite easy for you, but sometimes developers aren't really good at mathematics these days. Maybe in the '70s and '80s where all mathematicians and physicians did a bit of programming, it was quite obvious, but these days it's IT programming. It's a bit of a separate skill, Sometimes it doesn't translate directly to mathematics. But if you notice here with this y value here, let's take the number three. For example, if we multiply three by two, we get six. And then we subtract one from that, then we get the value five. Again, maybe four. For example, four times two is eight. Subtract one is 75 times two is ten, subtract one is nine. And I think that's a rule that might work all the way across the field, but we should always test with 1.0 in cases like this. One times two is 21 is one. Yeah, that seems to work too. I think that might be a rule that works. What we can say is p is equal to y multiplied by two, take away one. That is a rule that should work for generating the pyramid based on the line number itself. There might be a lot more solutions to this problem, but this is certainly one that would work for us based on y right here. Coming back into our software, here we have the value of y on each iteration of the loop. What we do here, we want to generate the pyramid on each line when y is three, for example. Then we want to generate five of these pound symbols. Here we said that is Y multiply by two and then subtract one from that. It would look something like this. I believe this would work, but to add a bit of clarity, I always use extra brackets like this. It just makes it more readable so we can see what's going on. But you would get the exact same result using this due to bid mass, because multiplication comes before subtraction. But in cases like this, I would always write it like this. For example, let's take a look at the example now and see what's going on. If we output the number five, input the number five, you can see now we get a nice pyramid. That's pretty cool, isn't it? Does this work for bigger numbers? Let's say 35. That looks pretty good. Yeah, it looks like it's working. You can see this is how I would approach a problem on something like this. We pretty much wrote 90% of the code by just analyzing the problem. We didn't need to really think about C sharp and programming. We literally just looked at the pyramid, dissected the problem a bit, and broke it down into smaller chunks. The only bit that was difficult was finding out the bounds for these four loops. So how many hyphens we should draw, how much of the pyramid we should draw on each line, and again, the hyphens on the right. And also a little complication about new lines and things like that, which is kind of normal. Sometimes everybody makes mistakes, it's normal. But you can see how we isolated these problems and used Microsoft Excel to sort of run the figures, so we didn't really have to hold all of this information in our head. We can just sort of take the problem here, dissect it all down, run all the figures, then we just have to work out how to get these figures from the information we have, either the height of the pyramid or the value of y on each iteration of the loop. So you can see how we broke the problem down without really thinking about it. We didn't really use any brain power. Everything in our mind was dumped into Excel and we can sort of work out a solution from that. So that's how I would tackle a situation like this. Especially if I was really tired or hung over and I couldn't think, then, you know, let the tools do the work for you. So coming back into visual studio now we're drawing pretty cool pyramids. We can even replace the background with a nice empty white space. And maybe we can draw two pyramids. I mean, we put it in a method, so now we can repeat the method a lot more easy. And that's the power of methods. So if I now put in the number five, for example, now we're generating three pyramids on top of each other. That's pretty cool, isn't it? So anyway, that's how I would approach a problem like this. Again, it's a common thing you may find in job interviews. But really the power of a programmer is to test logical thinking. How does your mind work? A good programmer is not somebody that can remember syntax and regurgitate information. A good programmer is someone that can think logically, break down a problem, and find a suitable solution. That is what a good programmer is. So I hope you found this exercise useful, and thank you for watching. 53. 10-2. Solutions, Multiple Projects and Namespaces: In this tutorial I'm going to be showing you how to set up multiple projects in visual studio. I'll talk a little about the terminology like solutions, projects, assemblies, and also name spaces. I can show you how to access files from different assemblies as well. This will be very useful moving forward. If we open visual studio, we can get this dialogue here where we can create a brand new project. Here, we're going to click this, then we're just going to create a console application. If I click next here, it's going to ask me for the name of my project. Now because I chose a console application here, this is what represents like a graphical user interface, something the user might see. Similarly, you could have a Windows Forms application, which is also a Gooey. But this is the graphical user interface projects because it has a window that we can see when naming this project. For example, it's quite common in applications to have what's called a three layered architecture where you have one project representing the interface. Maybe on a website that might have HTML console application, it would have like the black window and any logic to do with that. And then you have a middle layer, sometimes called the business layer, and that has all the background calculations, all the logic, everything to do with the brains of the application. And perhaps the third layer will be like a database where all the data things are concerned. The ability of getting data from a database. You know, maybe it's paired to an oracle database or an SQL database. So all things to do with the data layer. This is what's quite commonly known as a three layered architecture. When you create this project in C sharp here in visual studio, first we're creating the guy here. And this is the console application in this example. So I'm going to call it something like that. Typically what I do and what other software companies do is when you create the guy, you might put guy in the name of the project. If the project was called test app for example, you might see something like this, like test app guy. Or test a guy. Or perhaps guy test Ap, something like that. From the name you know instantly that you're dealing with the guy, the graphical user interface. So I'm just going to do test Apoe, for example. You don't have to do it like this, but this is good practice and it's quite common as well. If you continue with your endeavors, you'll see this quite a lot. I'm going to create the project now. Here we have our guy. It doesn't really do much. It's just a black window that's going to instantly close. But this project here, if we come over to the right, this project here represents anything to do with our guy. Anything graphical that the user might see, anything to do with the guy, all of that is contained within here. You can see at the top here, we have a solution. Now, solution can hold a number of projects, maybe 102030, and we can add different projects in here. So for example, let's create a business layer. And this will have all the code, all the logic, all the calculations, for example. Again, when creating a solution, if it's just a small test project, for example, very tiny, maybe you're just doing a quick mock up, then having a three layered architecture is quite ambitious. It might not be needed, but if you know in advance it's going to be a large project or something that might talk to a database or have a lot of complexity. Then you do need to consider your architecture before you get started this create another project. Now we're going to create the business layer. So if I right click the solution Add, I can go to a new project here. And when choosing the projects, I already have my guy here, this console application. So I don't really want another one, especially right now, maybe in the future. It depends on my needs. Everyone's needs are different. But something for like a business layer where you have code and pretty much just pure code. Then you want something called a class library. If I click next here, I can call the class library again whatever I want. But if my application is called test app like that, we might have something like B L a business layer or LL a business logic layer or something like that. Something representing a different layer in the application. Typically I would do like business layer for example. Then this project would contain all of the business stuff, like the business end of the system, if you see over here. Now we have two projects. We have our graphical user interface. Now we have our business layer here and that will contain all the calculations and things like that. Now lastly if I write, click the solution again. I could add something like a data layer, maybe a database project or something like that. It could also be a another class library representing the data layer. Something quite like that. You could say Dow for data access layer or something to do with data. Or even DB for database. It doesn't really matter. I could call it something like that. Then this last project here, this third one, would represent anything to do with tying our solution to a potential database, whether it's Oracle, SQL, my CQL, something like that, it doesn't matter. And now we have three projects. Now, architecture, There's so many architectures available when building software, like when building a building. There's not one way to build a building. There's so many different ways, but this is a very popular one. What happens is if maybe you have 50 people on your team, you work for a company. Some people will know about HTML for example, but they're not going to know anything about maybe a database or complex C sharp calculations in this project. So what happens is they will only work on this project. Similarly, if you're a database person, then you will only work on this database project here. Separating your solutions out by different projects also helps with teamwork and things like that. Only people knowing about the database, for example, would work with this database project. That's kind of like some of the reasoning behind it. How do I get my project here, for example? This guy, How do I get it to talk to this project? Because by default I've added three projects here under the solution, but none of them are talking to each other. How do we achieve that? If I go to my graphical user interface, for example, this project here, I go to dependencies here. Now, depending on the version of Visual Studio, this is the newest one, right now, it's called dependencies. If you have an older version, it might say references or something like that. If you right click that and go to Add Project reference. When I do that, a window appears. Now I can see all the projects in my solution as denoted by this left hand menu. Here I want to check the projects that I want to tie to my guy, say I want to talk to my business layer where all the calculations are done. I just check that there and press okay. And now internally, my graphical user interface, this can now essentially talk to this project here, the business layer where all the calculations will be. Let's put a sample in here so we can just do something. It's not going to do much. Set up a very simple method here inside what's called the business layer. And what that is going to do is just going to return the string hello. That is all it's going to do. I'm going to call it hello. I'm going to call it hello class. Now inside our business layer over here, I have a class called hello class. It has one method, and all that method does is returns the string hello. Now if I go back over to my graphical user interface project here, test app guy and I type in, for example, hello class. You can see it's not even in this list, but I've actually referenced the project to this one. Why can't I access it? Well, this is where name spaces come in. If you've been following these tutorials so far, you'll see this keyword name space quite a lot, almost in every file. And then it has a name. Typically the name of the name space is automatically generated from the name of the project. For example, this project here is called Test App Guy. But if I go over to my business layer, my business project I created, you can see it's taken the name of the project here. Now name space. It's just like a logical way of organizing things. For example, we've talked before about the math class, for example, where we do math art, absolute or square root or something like that. But the math class, if I hover over this, you can see it belongs to a name space called system right here. By default, when I create a new project in visual studio, I'm given some name spaces by default. All of these name spaces here, these seven, are provided to me by default. Essentially, I can use any code which Microsoft have provided me which is contained inside any of these name spaces here, just like I have a namespace here with a name. And I have some code in here. By default, I can utilize any code inside any of these name spaces. This is very similar to what we have here. What I need to do, well, I need to talk to the name space where I have defined that method, because right now it's not. Here. You can see where we've defined the method is inside a name space called test app PL. If I copy that, I go back to my guy layer, right here, right above here, I use a special word called using what? Using does, it allows you to use a different name space. If I just paste in that name space here, followed by a sam colon, if I type hello class, now you can see I have access to that, essentially by using this name space. I have access to anything inside this name space, inside this file. I hope that makes sense now, because hello class is defined in test at B L namespace, as you can see right here, it's inside the name space. I can access all of its features. I'm going to create a new instance of hello class right here. Now I can say hello, return hello. And that will get me that string. This is how I can talk to a different class inside a different name space, which is inside a different project. Now for ultimate clarity, if I come over to my solution here, I go to my test app business layer here. And I go to a class here, for example. You can say it has the default name space. If I create a brand new class, I go right click, Add New class. I call it whatever I want, it doesn't matter. You can see again, it has the same name space because it's taken from the project. It doesn't matter how many classes I create. By default, it will take the name of the project for the name space. But you can rename the name space to whatever you would like. You can see that's the power of namespaces. In shop, you can have nested namespaces, For example, a namespace inside a namespace, which is quite common in visual studio. You can see there's a namespace called system inside of that. There's one called collections. Inside of that, there's one called generic. Think of a name space as a way of grouping things together. If you have anything inside a project, which is to do with one project, all your code, for example, in the business layer, like the heart of the application, that will be one project, one assembly for example. However, inside that project, you might have different things. Like you might have part of the project to calculate the area of a house or something, but inside that project, you might have something completely different, like calculating a tax return. But maybe those two things might have to exist inside the same project for whatever reason. And in that case, you would logically group them in perhaps a different name space. So anything to do with working at the area of a house, you might call that one name space and the other one for doing tax returns or whatever The example could be anything and that could be a different name space. So you're kind of logically grouping by maybe an activity or a function or whatever you decide when thinking of projects, think architecture, like how you structure your solution. But when thinking of namespace, think of more logical things like how you group similar pieces of code together. And that's sort of the difference in this case. So I'm just going to show you one more thing with regards to multiple projects, and assemblies and things like that. Now, this is quite a complicated subject, quite a large subject really. But what I'm showing you is enough to kind of follow through the remainder of these tutorials. But not only that, but when you start your own solutions and projects, you have a general idea of how you're supposed to structure things. And also how to organize your code, which is very important the bigger your projects become. Now if we come over here, we have our solution here with our three projects underneath. Now each one of these represents like an assembly. It's a word you're going to hear a lot, but when people talk about assemblies and the internal access modifier, then it's internal to the assembly, which is typically represented by a project. One project per assembly. Now if I come over to this green play button right here, when I click this, our solution is compiled, all of our projects are compiled, and an assembly is created for each of our projects. So if I go to my file system now, now I'm using a window system for the guy project here. It's making a EXE file right here. Again, some various files with that. But you can also see it's actually creating a DLL file here for each of our projects. Now these are what's called assemblies here, because we have three projects in this case, we also have three assemblies here. You can see behind the scenes and how this is represented in the real world. When you give this software to your friends or maybe package it up into a set up file, you can see how these projects are represented as binary files right here, typically one for each project. One thing I will mention is that having this using keyword up here is somewhat optional if I decide to remove it, for example, you can see this is no longer going to work because it cannot locate the name space where this class is contained within. What we can do in this case is just qualify it with the name space. Every time I use Hello class, I have to tell the system where it's located, like what name space is it within? In this case, I can qualify it with the name space before the class name. But if I keep using this class in this file maybe 1020 times, I'm going to have a lot of kind of redundant code here. So rather than doing that, I can remove all of those and just kind of use the name space at the top of the file. And then I no longer need to qualify it every time I use it. So that's an advantage of using the namespace here, NC Sharp. 54. 11-1. Breakpoints and Code Stepping: Debugging, debugging in C Sharp. What is debugging If you've been following along my tutorial so far, we've worked with the C Sharp language, we've done lots of different things. Object orientation, loops, calculations, methods. But during these exercises, for example, and working with the language, the fact of life is that humans are human. They're going to make mistakes, whether it's intentional or unintentional, or just a total accident. These things happen. This is where debugging comes in. Now, debugging is a loose term. The word debugging is used in two different senses. We can say, okay, I'm going to do some debugging, and this is the process of trying to find bugs. Maybe your software has no bugs, but you're going to try and find some just to make sure it works correctly. This is quite normal. You also might use the term debugging when your software has a problem and you're trying to locate the problem. So you would say, I'm going to try and debug my software because there's an error. I don't know where it is, but I need to try and find it. So it's used in two senses here. Now, like I mentioned, the fact of life is no one is perfect. If everyone was perfect, then software companies wouldn't even hire test teams to run tests. You wouldn't have something called unit tests. You wouldn't need to test your code. But the fact of life is we're not perfect. And this is why we need to know about debugging and to try and find errors in our software. Now, so far in this tutorial series, we've been using Visual Studio. Now Visual Studio is great. It contains many tools, features, and we've barely scraped the surface, to be honest. It has a compiler that compiles our code. It has the IDE where we can actually type in to create projects solutions. It has that autocomplete feature, also known as Intellisense. So lots of different things, but one other thing it also has is what's called a debugger. So a debugger is a piece of software, a totally separate program, written by Microsoft. And the job of the debugger is to attach itself to another piece of software. This is called attaching the debugger. So what software does this debugger attach itself to? Well, this is your code, your software. Every time you hit that green play button, your software compiles in the background. If you're using Windows, for example, it compiles into an EX, for example. Then the debugger can attach itself to this EXE file in this case, but not only your software. It can attach itself to another executing process which your system is running. It's quite powerful. So what is the benefit of this debugger attaching itself to your software? What is the purpose of that? Why would it do that? Well, when a debugger attaches itself to your software, it allows you to exercise a level of control while your code is running. And it can examine particular segments of code when things may go wrong while your software is executing. Imagine that you can pause your software at any point in time. Say your software loads, it's running a loop. For example, maybe a four loop, and you can just halt the execution midway through the loop. Say you have a four loop and it counts to ten. You can stop your software at a moment in time, for example, when it's just counted to four. So while the software is running, you can go into your code and inspect everything. You can see values of variables. You can even control the execution. So manually make that fore loop do two more iterations, for example. And you can do this yourself. Have you ever seen those superhero movies where the guy is really fast and the whole world is frozen? But because he's so fast, he can interact with people in real time. Imagine that to be like a debugger. The world is going about its business. But this superfast entity, this super fast hero, can kind of fly around at the speed of light and modify things and control things. This is kind of how a debugger works. It's quite powerful and quite entertaining to use, to be honest. And the process of pausing your application while it's running using the debugger is called entering break mode. And when I said you can actually control the execution. For example, if your software is running and it's about to run a method, you can skip this method entirely by stepping over it and controlling the flow of your software while it's running is called code stepping. The debugger is actually quite a powerful piece of software, and 99.999% of developers would use a debugger in creating some sort of software. So let's take a look at an example of that. Now, how do we enter this world where we are a fast superhero? And we can pause the software and change things around, and change values of variables and skip methods and all things like that. How do we do that? Well, let's take a look. So if you've been following along our other tutorials so far, when we write some code, we've been pressing this green play button up here. When we press the green play button, our software runs. And when we want to kill it or terminate it, we either cross off the window here or press this red stop button up here. So that's what we've been doing so far. If you go to the left of this green play button here, you'll notice a drop down list here. By default it should say D bug, but underneath it also has release. Now these two items here are quite important. If we have bugs selected in this list, then every time we press this green play button, the debuger is also executed and it also attaches itself to our software. For those curious, if you select release in this list, then typically we use this when we want to give the software to someone else because it doesn't contain any debugging information. But for now, let's talk about debug here. Now this is called a release mode. Right now, we want to debug our program, we want to find some errors and do some detective work. Typically, when we develop software as a developer and we're finding errors and developing our solution, we would use this release mode here, bug. And this is why it's default. So like I said before, when we run the application here and our software is running in the background, the debugger, the visual studio debugger has attached itself to our software. And I can prove that to you if I Open Task Manager. Here's my task Manager here, these are all the applications I'm running. Here's Visual Studio, but underneath here you can see the Visual Studio debugger console. This is running in the background and this is actually attached to our software. But so far we haven't really made any use of this in our previous tutorials, but in this tutorial and the next few, we're going to be using this quite a lot. Now let's take a look at the visual studio debugger. Let's have a look at doing some debugging here. I have a sample application. When this main method runs. Here it's entering into a never ending wire loop. The application is never going to quit out. Every time this wire loop loops, we're asking the user to enter a day of the week. We're taking their answer, storing it into a variable, then passing their answer to this method here, depending what day of the week they enter. We have a switch statement that prints out a custom message depending what day of the week they enter. Quite simple, every time it outputs a message, we're just entering a blank line and then looping back again to ask them for another day of the week. It's quite a simple application with this application here I have a bit of a problem when I type in Wednesday. It's not giving me the actual output I want. When I type in Wednesday, I want it to output Wednesdays or myth, which it doesn't currently. For example, if I type in Tuesday, I get an answer for Tuesday. But for Wednesday you can see it's telling me I entered an invalid day. Now I appreciate this is a very simple piece of software, but imagine this software being very complicated. You might have 50 files. You might have methods, methods, calling methods, methods inside loops. So you can see it can get very complicated. So, let's take a look at how we can debug an application like this. We know so far using our detective skills that Tuesday works. So therefore, the code is coming into this method. The switch statement is run and we're getting an answer for Tuesday. However, Wednesday is not working. So, there's a problem with this code around this point. At least that's what I would think. So it looks like when I type in Wednesday, it's outputting this kind of default section right here. Why is it doing that? What I could do in this case is add what's called a break point. If you come over to this left hand side here, there's a gray bar. When I go anywhere in this gray bar, you can see a gray circle there. If I click with the left button, it adds a red dot. So you can see right here, this is called. What's setting a break point? Why is it called a break point? Well, when I run the software here and type in any day of the week, you can see the code execution stops to remember when I explained to you what a burger was, and I said, it's like that superhero that can modify in real time, you know, like the speed of light. This is the debugger inaction. Now the debugger has attached itself to our software by setting what's called a break point, these red dots. Here, we can set as many as we would like. Every time the code reaches one of these red dots, the software will freeze. It will stop. Nothing more can be done. If I try to open my software, I can't interact with it at all. It's totally frozen. And we have full control at code level. This yellow piece here, this is what it's frozen on. And that's our first breakpoint. So nothing else can happen. It's frozen in time. So what we can do while it's stopped here, we can actually inspect things. Look, if I hover over this, I can see the value of our variable here. I can see the value of it getting passed here. So it's pretty cool, isn't it? It's like interacting with the world while the world is frozen. You know, feel the power. So this is the power of a break point. It breaks the software. And I don't mean break like break a glass cup or break a glass vase. I mean, breakers in pause, like halt. Halt the execution. So that's what a breakpoint is. The next thing I want to talk about is what's called code stepping. What is code stepping? Right now, our software is frozen in time. It's frozen at this line right here. The switch statement hasn't been run yet. It's yellow, which means it's about to be executed, but not yet. What we can do, we can manually execute the next line of code. This is called stepping, and we can do this manually. If we come up here, you see all these icons here. This one here, it says step into, this one step over, this one step out. And this one step backwards. So lots of different stepping buttons right here. But what is stepping? Well, for example, this one here, step over. You see the keyboard shortcut here is ten. If I press ten, that's going to step over this statement. And what that means is the code is going to execute to the next line of code, or the next block of code inside a switch statement. Here is taking in our input, which is pretty much a garboard string. What should happen is this line of code would be run because we don't have any day of the week matching our input. If I press F ten, which is step over, you can see the code then goes to this line right here. Now we've executed the start of the switch statement, and now the software again is frozen in time. On this line, you can see we don't have a break point on this line, but that doesn't matter because we manually stepped over. If we want the software to continue executing, then we would press the play button, for example. Then the software would just keep running until it hits one of these red breakpoints. But when we do code stepping like step over step into all that kind of stuff, we're manually executing a line of code at a time, or a block of code at a time, like a switch statement, for example. So that's the power of stepping, and that's just manually running segments of your code in sequence, how it would normally be executed. Now the software is frozen on this line here. You entered an invalid day. If I press ten again, then now our console window will display this line. If I open the console window, you can see this line has now been executed, but again the software is frozen in time. Again, on this break symbol here, I press F ten again, and now we're about to write this line to the console F ten again, and now the method is executed. That's pretty cool, isn't it? Stepping in visual studio when working in C sharp is to manually control the code, manually execute pieces of code. That's what code stepping is. It allows us to manually execute lines of code. And we can do this ourselves. And we can do this by setting break points to initially halt the code. And then we can use what's called step commands to step into, over out and all things like that. But what is the difference between step into, step out, step over? What are these things? Well, consider this example here. We've run the application, and I'm calling this method five times in a row for no real reason other than to show you the difference. If we run step into which is 11, then we're going to step into this method. If I hit F 11, you can see the next line of code to be run is the open curly brace right here, followed by the switch statement. I've stepped into a method, I've stepped in here. What we can also do is step over the method. Just ignore all this completely. Maybe we know this method is perfect, there's nothing wrong with it. So we can step over this entire method. And then the next line to be run will be this one here. Because we've steps over the whole method, that's the difference between step into and step over. We can just skip a whole section of code. You may have guessed it. What is step out? Well, we're in a method right now. I can click step out shift 11 and we can completely step out of the method. And we do that when we assume the rest of the methods. Fine. We kind of want to step out of here and get back where we were before and then step into anything else. So that's the difference between these step commands. Typically it's just step into something like a method, or a class or something like that, or a property, or we could step over it completely. So just ignore it and carry on with the rest. And if we find ourselves in a method and you know, everything looks kind of good, then we can step out of it. So these are called step commands. And the process of moving the codes execution is called code stepping or stepping. So that's the difference with those there. So now I've explained breakpoints. Code stepping, stepping commands. Let's try and find our problem here. It may look quite obvious, but remember we said Wednesday wasn't outputting the correct message. So why is that? So let's set a break point on this switch statement here because we know the problem is likely to be inside this switch statement. So I'm going to run the application now, and I'm going to type Wednesday. I'm going to hit Enter, and we're about to launch this switch statement. Here's our variable here. I can hover over input, and I can see, look Wednesday. So now what's happening is if I step over here, you can see it's hitting this default case. So none of these cases are matching Wednesday, but which seems weird because I have Wednesday right here right now, Wednesday. So if I hover over this variable, Wednesday, oh, I see, look, the y is in a capital right there. It's upper case. That's probably why now I've changed this y to lower case. I hover over this variable here. It looks like it matches correctly. So this should work. Now what I could do is restart the application. You see this icon here next to the Stop button. It says restart. What I could also do is stop the program or cross it off and then run it again. This restart button here, what that does, it restarts R code, but it leaves the debugger running in the background. If you click restart, especially if you have a large piece of software, it's slightly quicker to get going again. That's the difference between the restart and the stop play button. One thing we can also do, for example, is to manually move the code's execution. What the hell does that mean? Right now, we're executing this line of code. It's just about to be run. We just step over that, and now we're about to execute this line here. Essentially this switch statement here is finished executing. What we can do is hover our mouse over this yellow arrow right here. Hold in our left button, and we can actually move the codes execution right back to the start of the switch statement, like it was never run in the first place. That's pretty cool, isn't it? Imagine dragging the mouse here as using a step command, like step over or into. But it allows you to step back, but not only one line, but multiple lines. So it's a short cut for those step commands. But it allows you to do it in big chunks, for example. Now we're about to re, run the switch statement again, but we've actually modified the code here and we haven't even stopped our software. It's done in real time. It's pretty cool, isn't it? Now, if I step over using ten, you can see this line is now hit right line. Wednesdays are mere, so it looks like we fix the problem. It was just, it was just that upper case y on Wednesday. So now what I can do is just press F five, which is short for this green play button. So now I think the problem solved. I don't want to do any more debugging. I can take away my break points if I want, and then I can just hit this green play button and that'll just let the software continue as normal. So now it's saying Wednesdays there, which is perfect. That's exactly what I want. If I repeat it again, we get exactly the same result. So it looks like we fixed the issue with our software. It was just a one character difference. It might be a minor change. But even things like a one character difference can bring, say, space X rockets down to the floor, never reaching orbit. So it is very important that everything is checked in pure detail. In order to do that, a debugger is a very useful tool on how to accomplish things like that. I'm going to introduce one more example and a couple of other debugging tools you may find useful. They are run to click and run to cursor. So let's take a look at this example here. If you followed along the previous tutorials, then you probably remember this example. Essentially, this example is being asked for a number. You type in number 25, and then it draws a pyramid which is 25 lines high. For example, because I put 25, it has 25 lines high. But you can see there's a problem with the background for this pyramid. This right side here is going on too long. It should look like the left side here. After each line, you can see the pyramid grows wider, but the background shrinks just like this. But this behavior isn't being mimicked on the right hand side. There's a bit of a problem with this. Let's take a look at what's going on here. Here's the example. Here we're asking the user for how high they want the pyramid to be. We're passing it into a method. We're delegating all the logic of drawing the pyramid in this one method. Here we have our main four loop that draws out each line of the pyramid in turn. Then we have 34 loops, one to do the hyphens on the left, one to draw the pyramid, and one to do the hyphens on the right. We know we have a problem with the hyphens on the right. This is probably a good area to set our breakpoint and have a look what's going on here. If we run the software, we ask the user for a number. Let's start out with a low number. Low numbers are easier to debug because there's not many of them. I'll type in the number five. Our breakpoint has been hit here. Right now, H isn't declared. Let's press ten to step over. And now we've initialized the header for our four loop. Right now we're about to do the first iteration of the loop. H is one because that's its initial value here. Then H is going to keep running until it's less than or equal to what looks like five. And every iteration we increase by one. For the first line, H is going to continue five times because that's the size right here. If I step over that, we're outputting one hyphen, then two hyphens, three or five. Then it's done. The very first line on a pyramid, which is five units high, outputs five hyphens on the right. Is that true? Is that right? No, because on the first line, it should output four. It's generating too many hyphens here. Why is this? It's obviously generating too many hyphens, but the hyphens on the left are generating the correct amount. So you can see here, the hyphen should stop when it's size minus y. That's the formula we had in here. We've obviously done it for this hyphen loop here, but we've neglected to replicate the same functionality for the hyphens on the right by using a break point. You can see that we can examine the value of H while the software is running. Let's just do that now. You can see we can examine the values of H. We can examine the values of size, We can examine the values of y. We can even examine values up here, values coming into the method using the step commands like step over or into, we can actually control the execution of the software. That's pretty cool, isn't it? Let's say we've figured out the solution here, we've figured out the problem. Now, I mentioned a couple of things before about run to cursor and run to click. What are they? Well, run to cursor and run to click short cut commands. Remember when I talked about dragging this yellow arrow here? Right up here so we can control the execution? Manually run to click and run cursor short cuts for controlling the code flow. Like code stepping. If I put my cursor here, for example, right click and then I choose run to cursor, click that and then the execution goes to wherever my mouse cursor was. It's a bit of a short cut and it's quite useful. Another one is run to click. You can see when every time I click a new line, this mysterious little green play button appears. But you can see here, this one right here. I click this line, it appears right here, it's like a bit of a green ghost. So this is called run to click. If I click this little green play button here, the code execution is going to jump to this line. So it's pretty much the same thing as clicking this line right Clicking and choosing run to cursor. So it's just a nice little handy shortcut. So you can see run to click and run to cursor are both handy little shortcuts. If this section of code repeats multiple times, then I can click this for example, and the code execution will then keep going until it reaches this line. They're just nice little code stepping shortcuts. This one is run to click and the right click one, you can do run to code cursor, but there is a shortcut for that as well, which is control F ten. The more you use visual studio, the more you're going to learn these shortcuts. But every developer I know anyway will know step into and step out, which is F 10.11 And those two are really useful for stepping through code. So now we're going to run the application and it looks like our issue with the hyphens has been resolved. It was just a problem with that last four loop here. And that's the upper bound. So when debugging code in general, you have to ask yourself a few questions. If an error occurred, what was the statement or expression the program was doing at the time of the error? What line of code did your program fail at? Did the program fail? And you had that kind of highlighted line that said there was an error there. What line was it? And when your program failed, what were the values of the variables, like the parameters, the local fields, any objects? What were those values when the error occurred? What were the sequence of statements executed at the time of the error? Were you inside a method? Of a method, for example? So, where were you? What was executed beforehand? And I think I've pretty much covered this one. What was the result of the line of code where it failed? Or maybe the result of the line of code before the error? So you have to consider all of these things. You can't just put breakpoints anywhere and hope to find an error. You have to kind of ask yourself these questions. Kind of target the error roughly where it might be, what class it might be in, what method it could be in. Then once you've isolated it to a particular method, then you can start kind of plotting breakpoints and isolate it a bit. To summarize, this is what debugging is. It's the process of looking for errors, but if you have an error, it's the process of kind of isolating the error. This is what a debugger is. So this is a visual studio debugger. And you can use this when you set your release mode to debug. And when you are debugging, you can place things like breakpoints. And this is where the code execution will halt. When the code execution halts, this is called break mode. You're entering break mode and this is when a break point has been hit to control the flow of execution. Using step in to step out, rent, to click renter, cursor, or even dragging the mouse along this break point bar. Then this is called code stepping. These are all the, all the terminology to do with debugging in visual studio. You may be surprised, but we've only scraped the surface of debugging. I hope this tutorial helped you. Thank you for watching. 55. 11-2. Immediate Window: In this tutorial, we're going to talk about the immediate window. Now this is a debugging utility and it is extremely useful. If you haven't seen my last tutorial on debugging, breakpoints, code stepping, then I highly recommend you watch that before watching this tutorial, the immediate window, what is it? If we come down here, you can see this little tab here called Immediate Window. Maybe you've seen it before, maybe you've been wondering what it's all about. If you don't see this tab here, then if we come up to the top, we can go to this debug menu here. Now this is where all the debug utilities and features live. If you were wondering, go to Windows and then go to Immediate. And when you do that, we come back down here and this little tab should appear right here. Now, the immediate window can be used at design time or run time, so what does that mean? Well, design time is when we're kind of developing. We haven't even hit the green play button yet. We haven't compiled anything. We're not running anything. But what we can do, we can actually work with our software in design time, so the software is not even running. So let's take a look at this example now so I can show you what I mean by that. If you followed our earlier tutorials, we made a sample calculator where we ask the user for a first number, a second number, and then an operator. And then inside a method here, for example, it takes those numbers and an operator, for example, 54, and then maybe plus. And then if the operator is a plus, it adds them together and then just displays the result, which would be nine. In this case, what we can do, we can actually test this method from the immediate window. It's crazy, right? The software is not even executing, it's not even running. How do we do that? Let's take this method here. Calculate, for example. So I'll copy that. We'll come down to this immediate window here. Now, anything in the immediate window starts with a question mark that pretty much says, okay, I want to run a command. So I want to run this method. So what I'm going to do is call this method. I'm going to call it with five, and it takes a character, and remember characters in single quotes. And we're going to do a plus when working in the immediate window. The semicolon is optional. We can put it, we don't have to, it doesn't really matter. Now watch what happens when I hit Er. It actually runs our software, compiles and runs it, and then gives us the result for this method. You can see it actually did this at design time. My software wasn't even running it gave me the value nine. It's a pretty good way of testing things like methods, evaluating expressions at design time, but also run time as well. It can also do this while the software is running. That's pretty clever, isn't it? If I put a break point, maybe here for example, let's clear the immediate window, we can write, click that and click Clear. All that will just clear out the window for us. So now up here I have a break point on double result equals calculate. Before I even call the method, I'm halting the program, so nothing else is going to continue. I run the application by clicking the green play button or pressing five. It doesn't matter. Now we're asking for the first number five and then four, and then I want to add those together. Now the program has stopped executing. If I come down here, the bottom corner, I have this immediate window right here. So I can do lots of things here. I can run that method again. For example, while the code is running, One useful feature is while the code is running, we have this Intellisense, the Autocomplete. It's actually providing us all the variables in scope, like number one. Number two, we can pass it custom information if we want. If I say 54 and plus, just like we did before, then I hit Enter, we can actually get the result. But you can see here, nothing has really happened here. We can still continue with this calculation. That's pretty cool, isn't it? What I can also do is use existing variables. Right now I have number one, number one. If I go over here and highlight this value, you can see the user gave the number five and number two they gave four. And the operator they used a plus right there. What we can actually do is use those variables. We can actually see the result before the method is even executed. Well, maybe I want to multiply them. So you can see here five multiply four is 20. So you can see the immediate window can actually intercept various things. Evaluate expressions, run method, lots of things like that. All while the code is actually in break mode. This method hasn't even run yet, for example. Now there is one fine detail with that. In this immediate window down here, I've called the calculate method twice now. But imagine if calculate did something else, maybe it counted something in the background. Every time I run calculate it keeps a tally, a running total of how many times I've called it. Now running this method in the immediate window would affect the results. It's like this method is actually being run now that could cause various problems. So depending on what your code does, if you mess around in the immediate window here, it can affect the results up here. It just really depends what your code does. For something like calculate, well, it doesn't really store any information. It doesn't count anything. It doesn't keep a running total of how many times it's been called. So it's pretty safe to run in the immediate window. However, there are cases where it would be unsafe, for example, for those other reasons. That's just something worth noting. So let me demonstrate that. Now just to illustrate what I'm talking about. Let's say this calculate method does keep a running tally of how many times it's been called. But we use this running tally for important purposes. Maybe something else relies on it. This field is just going to keep a tally of how many times the calculate method is being called, when the calculate method is called, I'm just going to increment this local field by one each time. So if I run the application now, I'm just going to set a break point on here so we can pause the execution of the software. I'm going to type in some sample figures, like five plus four. And then I'm going to come over to the immediate window here. This hover over this private field here. Numb times, you can see the value is currently zero. But if I run this method inside the immediate window, this maybe run it three times. By the way, by hitting the up arrow on the keyboard, I can look through my previous things I've typed in here. So that's pretty cool, isn't it? So I've run the calculate method three times, but only from in the immediate window. If I come up here and hover over my private variable here, you can see it has the value of three things in your code are affected by anything you do in the immediate window down here. So it is really important and it's something you should be made aware of. Again, obviously, everything resets when you run your application. But as far as debugging goes, it is worth noting this. So I've just talked about the fact that when using the immediate window, for example, to call methods, can change things in your code. Now this could be wanted behavior, maybe you want to do this and that's perfectly fine. But there are situations like in our example previously where we increment a variable, for example. But we need this in here and we don't want anything in our immediate window to change this. But we do still want to run the method from the immediate window. Well, there is something we can actually do to overcome this problem in the immediate window where I call the method, whatever you put in here, whether it's calling a method, evaluating an expression, finding out the value of a variable, you can just suffix it with a little command called S E that stands for no side effects. You can see when I type that visual studio gives us some nice indication right now. If I come up here, you can see our variable here, number of times is zero. I come back down to the immediate window and I press Enter. So you can see Calculate has actually run the figures. It's added these numbers together, but I've specified this no side effects flag. If I come back over here and harver over a number of times, it still retains the value of zero by specifying SE, it means that no side effects are going to happen as a result of you calling this method from the immediate window. That's pretty cool, isn't it? That's one of the features you can do with that. So we've called methods with changes, we've called methods without changes. Well, what else can we do in the immediate window? Well, we can view values of variables. So for example, number one. What is that? Oh, number one is five. That's pretty cool, isn't it? So always prefix it with a question mark. And obviously, these are only variables in scope. So, for example, if these variables don't have a value, or they haven't been reached yet, or they haven't been initialized, then obviously you can't read the values of these. So it's only what's called in scope, what we actually have access to. What we can also do is evaluate expressions, for example, five plus seven for example. It will give us the result and we can do that with variables, so number one divided by number two. It's pretty cool, especially when you're debugging, you've put in some sample numbers, but you can halt the execution of the code and play around with it in run time, rather than restarting the application, Trying a few numbers, restarting it again, trying more numbers. You can see how the immediate window expedites that problem. You can just put in whatever you want and maybe you're trying to locate an error or an issue. It gives you a really fast, easy and dynamic way of trying to locate these problems and errors. This is why the immediate window is pretty cool in that sense. But not only can we just call methods and look at values, we can actually assign values as well. If we looked at the value of number one which the user entered is five and they enter number two, which is there six. And the operator was a plus, so we're going to get 11. What we can do is actually change values of variables. Rather than adding five to six and getting 11, they're say number one equals 11. Now number one equals 11. Let's make number two equal 12 for example. And we'll leave the operator as a plus. Now we've changed to those two variables. Let's come up here now. If we hover over those variables, you can see number one is now 11 and number two is now 12. We've modified the values of these variables during break mode while the software is running at the speed of light, like we were talking about before, we've actually modified things at run time. It's crazy, isn't it? It's amazing. Now if I press five and continue with the running of the software, you can see the result is 23. The user entered 5.6 but we kind of went in there, modified some stuff, changed this one to 11 and this one to 12. So you can see the result is the reflection of the change that we did in the immediate window. So that's pretty cool, isn't it? So imagine the immediate window is like a little notepad where you can play around and change things and call things. That's the power of the immediate window in visual studio when working with C shop. 56. 11-3. Locals and Autos Windows: Continuing with our topic on debugging, I'm going to talk about the locals window and also the autos window. What are they? Well, locals and autos windows are only available during a debugging session. We need to enter debug mode and take a look at those windows and then I'll show you what they have to offer for you. What I'm going to do now, I'm going to add a breakpoint. Here's my simple calculator application where I add, subtract or multiply numbers together. So various things here. I'm just going to set a breakpoint in here for no particular reason. Then I'm going to run the application in debug mode because we want to do some debugging, the software is running, it's asking me for two numbers. I'm just going to put some sample data in there. Now, the code has paused, execution, and our break point has been hit. Now the software is frozen in time, and we can do whatever we would like with it. If we come down here to the bottom left corner, in my case, you can see we have some tabs here, various tabs. One is called locals and one is called Autos. Right here. If you don't see any of these, then come up here to the debug menu, go to Windows. And then there's a couple of options here called autos and locals. Now, you may not see these menu options unless you're in a debugging session. So make sure you're currently debugging and these should appear. You can also use these keyboard shortcuts as well, once you have these windows visible down here. What these windows offer is a real time look at the variables when we looked at the immediate window before, where we could look at values of variables with the question mark. Before we imagine this being a graphical user interface for the immediate window in terms of reading variables and objects and things like that. Anyway, you can see I've paused the execution of the code inside this calculate method. Here we already have values for num one, num two, and also the operator. Our result is currently zero because we don't have a value set. So if we look in this locals window here, we can see all those values for those variables in one easy window. So we can clearly see what the user has given us and what the result might be. Not only that, if we double click the value here, we can actually change this information in real time, just like before in the immediate window, we can change these values. I go to result, I can even modify the result before it's even been initialized. And not only that change the operator, for example, it doesn't only give you a read only view, you can actually modify these variables and the changes will be reflected during your debugging session. So that's pretty cool, isn't it? So we've looked at the locals window here where we can view our variables here and also change some of the values. Now these are available in the current scope. So what that means is I've set a break point here. We're inside this method, this is the current scope. We can access these variables here, but we can't read anything outside of this method. It's just things in the local scope. What's local to us right here? This is what's reflected in the local tab right here. Let's talk about the autos window now and also how the autos window differs from the locals window. They are quite similar in the way they behave. You can change variable values and things like that. You can view the value of variables and objects, but why are they different? The autos window here, it displays information on the current line. When I say the current line, the current break point, you see the software is paused here, indicated by this yellow highlighted part. We can see variables and objects on this current line. Right here, we have the result. Not only that, we can view information on the previous line as well. Now we can see num times, and if I step over that using ten. So the code execution goes to the next line, you can see the information is changed in our autos window. Really the main difference between autos and locals is that autos gives you the current line and the one before it and locals gives you everything in the current scope. You can see the locals window here doesn't include non times because we've defined it up here. So you can see it's a static private field of our program class, so it's not appearing in the locals window. The locals is only the local things to you. The local things in the scope and the autos is the current line and the one before it. That is the main difference. But one thing I haven't discussed yet is that both local windows and auto windows can evaluate expressions. If I go to here, for example, where it says result, I can do what we did in the immediate window before where we evaluated certain things. I could say the result is five plus four, so you can see the result is nine. I can also use existing variables. Number one, for example, plus 567 and that will get evaluated, so you can also evaluate expressions in both the locals and the autos windows. I've set up a sample application here that uses some more complicated objects. I have a video game class that gets passed in some things into the constructor. I have a list of users, and I'm adding three user objects to that list, and also creating a list of integers. So quite some complicated things in here. I've put a breakpoint at the very end. So we're going to enter a debugging session, and then our breakpoint is going to be hit, and then we're going to look at the locals window to see what that might look like. I'm just going to extend this up a little so we can see a little better. You can see here, this is pretty much everything here. Now I have these arrows Look because these games are more complicated objects. I can just click this arrow. I can actually see all the properties and various things inside here. Now this little one has a padlock on it, which means it's a private field here. But this has a little wrench on it, which means it's a property. I can modify the values inside here, so you can see I can use a text visualizer to view that, so I can look at the values of the title. If I double click the value, I can modify various things here. I could say that one's for a Macintosh, just like before when we had simple variables, simple value types. I could change the values. But even with complicated objects like this, I can also change the values and view the hierarchy of those as well. For this one right here, the user's list, I can expand that. And then I can expand the members inside there and see various names and ages and things like that. So it's quite useful and really powerful. During a debugging session, you can view the state of all of your objects, whether they're complicated or simple value types, or within one graphical window right here. It really is amazing. And if we look at the autos tab, I said the auto tab displays information on the current breakpoint and also the previously executed line. In this case, we added a breakpoint on this red line. The last statement that was run was this line right here. Therefore, this object is made available in our autos window. If you have a really large piece of software, perhaps with hundreds or thousands of objects and variables in the current scope, then you can actually search for them too. So it's really quite useful how that works. And you can specify a search depth, which just means how many can arrows where your search results may appear. So you can see there's a lot of depth options in there as well. But that is really the principle behind the locals and auto windows. It allows you to view and also change variables. But unlike the immediate window over here, it gives you a nice graphical user interface to work with. And also gives you the state of what these objects are like, are these private fields, are these public properties. So it really is quite useful in that regard. 57. 11-4. Watch Windows and Quick Watch: I'm going to talk about watching now, and this is again related to debugging in visual studio. What is watching specifically? I'm going to be talking about quick watch and watch Windows. So what are they? If you watch my other tutorial on locals and autos Windows, it kind of works very similar to that. The only difference with a watch window is that we can choose what to add in there. But not only that, we can evaluate expressions. So what does all that mean? Let's check it out. So right now I have a sample application, our little calculator application. If you've been following our other tutorials, I've just added a random break point here. I'm in debug mode, I'm entering a debug session. The debugger is attached to our software. It's asking for two numbers and an operator, five plus six. Now our break point has been hit, the software is frozen. We can examine the variables right now. We come down here we have our familiar locals window, where we can look at the value of the current variables in the current scope. Number one is five, number two is six, the operator is plus, and the result is 11. These are values of all the variables in the current scope. Now watch window. If we come up here to debug and then go to window, and then you can see there's watch 123.4 That means we can have up to four watch Windows, four sessions. Let's talk about what a watch session actually is. I'm going to click Watch One. And if we come down here, you can see there's a Watch One tab which has been created alongside locals, autos, and now we have a Watch one. And you can see here it says add item to watch. What does that mean? Well, we can watch anything. We pretty much want to like variables, objects. For example, if I come up here to the code, we have these variables here. Number one is number two is six. If I right click number one, I can come down this menu and click Add Watch. I'm going to do the exact same thing for number two. Right click, Add Watch. If we come to the watch window down here, we can see it works pretty much like our locals window. We have the variables we've added, we have the values, and also we can change the values if we want to. You might ask yourself, why don't I just use the local window? It does exactly the same thing. Pretty much the main difference between the watch window and the locals window is that watch, you can add whatever you want and also you can add expressions. For example, I could say number one plus number two and then hit Enter. I've added a custom expression here. Now through the lifetime of my pretty much debugging session, I know that the value of num one plus num two, or I've put number one there plus number two. If I can learn to type is 11. You can see I can put expressions in here. I could say number one multiplied by the result. I can put various custom things in here. This is pretty much one of the main differences between the watch window and the locals window. What were those watch 1234 windows. If we come up here to debug again, then Windows, then watch and click Watch to come back down here. Now we have another watch tab, then we can add other variables here. Now these extra windows are pretty much only useful when you have a really large application. You want to isolate certain variables from other variables just so they're more organized and you don't get confused. If you're working on maybe a calculator application, you might want to put all your watched variables in this watch window. Maybe the calculator application has another feature that handles something totally different. And then you put your watch variables in here. You're organizing your variables and expressions. You can have up to four watch windows if you wish. That's one of the benefits and powers of the watch window. Not only you can view and change variables like the local windows, but you can also add expressions in here. That's pretty cool. You're not limited to just basic variables. You can even call methods. For example, I have a method called calculate. And then I can calculate, say four plus eight for example. And then I can put that in there and that gets evaluated as well. Expressions aren't just tied to simple variables, but we can just put entire method calls in here too. It's really powerful and also really useful especially when debugging quite large applications. And one thing I mentioned at the start of this tutorial was Quick watch. What is Quick Watch? Imagine you just want to watch one simple variable very quickly. Say you just want to check out one variable's value real quick. That's pretty much the only purpose of Quick Watch. If I write click number one for instance, and click Quick Watch, or shift F nine, this window appears. And when this window appears, you cannot continue debugging. You. Pretty much just stuck in here. In here I'm quick watching the variable number one, I can change its value, I can re evaluate anything I wish. And I can also change or enter any other expression. So I could say calculate. And it does have autocomplete in here as well. So if I want to say five plus four and hit Enter, I can do quick expressions on the fly, but you get this kind of annoying dialogue. And to be honest, I prefer just using the watch window because it does everything the quick watch does. But I'm just highlighting it 'cause I know some people prefer to use that. I'm not sure personally why. But it is there if you need it. So that's essentially the message I'm trying to get across. But the watch window does everything quick watch does. So that's the powerful of watch windows in C Sharp. 58. 12-1. The protected Access Modifier: I want to talk about the last access modifier that we haven't already discussed, and that is protected. We've talked about public, private, internal, but now we're going to talk about protected. Now, protected is a key word which is generally used when you're inheriting classes in C Sharp. So if you haven't seen the tutorial I made on inheritance and while we're at it, if you haven't seen the tutorial I made on setting up multiple projects in visual studio, then I highly recommend you check those out first. Here we have a very basic example. I have a main class here. It just sets up four video game objects here. If we look at the video game class here, not much is going on. It has one private field and a constructor and it inherits from a main game based class here. And it calls the games constructor from here. Very simple, nothing we haven't seen before. If we look at the base class, it has three private fields. It has a constructor, it has a sample public method, and a couple of sample public properties here. Here we have lots of public things going on here. Now, the protected keyword, it applies to methods like this one and properties as well. If something is marked as protected, then it's only available to the current class, for example, game and anything descending from that, all of its children. Think of it. If you're like the mother of a family, then you only want to share protected things with your children or your grandchildren for example. So think of it like that, it's protected right now. This is a public method. Here. All it does, it gets the name and join some strings together and the publisher, right now, it's public. So we can access this from anywhere. We can access it from our main program. We can access it from video game, no problem at all. What I'm going to do, I'm going to make this protected, So you can see there's the protected keyword. Now I've done that. If I instantiate this class here, game from the main class here. Now the main class isn't a child of that class then it's not going to. Let me do that, let me prove that to you. Now you can see here when I try and access the method, it's not even in this list at all. And watch what happens if I try to access it anyway, ignoring Visual Studios autocomplete. If I hover over that, it says it's inaccessible due to its protection level. And that's because it's protected. So it's only available from the current class or the child classes of this class. For example, video game, Video game is a child class because we're inheriting from there. If we just say base for example, then we're accessing the base class which is game. Now we can see this method, it's in the list, and when we try and access that, there's no errors at all. That's the power of the protected keyword in C sharp. But there's a couple of combinations that can actually go with protected, and that is protected internal, and also protected private, protected private, and protected internal. These are a couple of combinations we can use when dealing with the protected access modifier. So we can basically double up access modifiers, but only when using protected. You can see here we can use it in three combinations by itself, which is what we've already discussed. It's available in the same class. Methods and properties are available in the same class or any of its children. We've discussed that next, protected private. If something is marked as protected or private, a method or a property, then it can be accessed in the same assembly, but also from within the same derived class. If our game class here is in the same project, the same assembly as our child, which would be video game. If these exist in the same project, the same assembly, then we can make use of those methods. However, if this game file here was in a different project, then we cannot access the methods and properties from this child class that is private protected. So let me show you an example of that. Now I'm going to mark Publisher. This is a shop property here. Publisher, I'm going to market as private protected. Now if this class exists outside of the calling assembly, wherever we want to use this, it's not going to work. Let's have a look at an example of this working. We can say publisher. We can access this, no problem. If I just say string something equals publisher, there's no problem because we can access it. Now let me move this class here. Public class, main, outside of the current assembly. If you saw my tutorial on multiple projects, you'll probably know how to do this. If we come over here to the right hand side, we get our game class. The parent class, I'm just going to drag and drop into the second project I have set up. The principle is I just don't want it in this project anymore now, I'm going to delete it. Now game is in this totally different project over here. Now game is in a totally different assembly over here. We can come back to our video game class here, which is in the other assembly. Go over here now you can see an error has occurred. So it can still find game because we're referring the other projects, so it knows where it is. You can see we're inheriting from there. However, now a red line has appeared. And if you hover over that, it says publisher is inaccessible due to its protection level. That is because we've made it private protected. If something is private protected, it has to be within the same assembly, so the same project. And it has to be a descendant of this class that is protected private. Now we understand protected private, the same assembly and a child, it's very easy to explain what protected internal is. That it can be a, any descendant of the class, but it can be in any other assembly. It doesn't matter where, for example, base class is located. It could be in a totally different project. But as long as it's protected internal, we should be able to access it. Right now, we have this error because of protection level, because video game and game are in different assemblies. I go back to game, I now make this property here, protected, internal or internal protected. So I've set that up there I go back to video game, and now you can see the error has gone away. So that is the difference between private protected and internal protected. It just means the base class has to be either in the same assembly or not in the same assembly. So those are the three access modifier types when dealing with protected, so the base class and its children. And then we can double it up with private or internal depending on if the base class is in the same assembly or a different assembly. So that is the protected access modifier in shop. 59. 12-2. The static Keyword: Now I'm going to talk about the static keyword. You may have seen this if you've been following our other tutorials. This little keyword here called static, what does that mean? What does it do? And why should we use it? Let's take a look at this example here. I'm just defining four video game objects here and calling the constructor with three parameters. If I look inside the video game class, it just has three private fields. Here's the constructor that sets the private fields. I just have an example method here that returns the title. And just an example property here that just gets the publisher very basic. If I have a class like this, for example, how would I perhaps keep a tally of the number of video games I have in my collection? This is just an example what I could do every time I instantiate the video game class. I could keep track of a counter. This counter can keep a tally of how many video games I have. In my collection, I initialize a counter to zero. Every time I create a video game, I can increment the counter by one. I could do something like this, for example. That would work perfectly fine. But it doesn't look very elegant, does it? Not only that, but it doesn't really follow the principles of abstraction very well. We'd like to keep this counter maybe hidden away in the video game class, for example. How would we achieve this? How could we do this if we set up a counter inside this video game class, for example, here. Then in the constructor for that class, I increment the counter by one. However, the problem is this counter will belong to each instance. So if I go over here and from game one I can access the counter, but it's only going to have a value of one because the counter belongs to each separate instance. So how do I have like a global counter, something inside this video game that keeps track of the number of instances of this class that we create. Now this is where the static keyword comes in. When we use the static keyword, we can use it on constructors, we can use it on fields, we can use it on methods, and we can even use it on the whole class. For example, for example, if I define this counter field as static, then this field will be shared across all of the instances which have been created from this class. It's a class level field. Anything with static inside the class will belong at class level and not instance level like here. For example. Let's take a look at an example of this. Every time I create a new video game here, I want inside my constructor here to have a counter that increments by one. This will keep a tally of the number of video games in our collection. For example, what I could do, I can just do a sample line here that writes to the console how many video games we have in our collection. Every time I construct a new object of the video game class, I'm incrementing the counter, which is static, it's at class level by one each time. Then I'm outputting a message to the console window that just expresses how many games I have in my collection when I run this program. Every time. This is constructed here because we're creating a new instance, the counter is going to increment by one each time. Let's take a look at that Now you can see here, it's incrementing by one every time this counter is being shared by all of these instances. Here, it's quite clever how the static keyword works. What we can also do, for example, is have a static method as well. For example, I can create a static method that gets the result of my counter. Let's take a look at that. Instead, I'm going to remove this line here. For now, I'm going to create a static method. What this method does, it just returns the counter. And it's a class level method, that means we access it from the class and not an instance. Let's take a look at that right now. If I go into the main program here, if I go to game one, for example, now game one is an instance. This method will not appear in this list. You can see there's no get counter method here. That's because it's a class level. In this case, I would have to type in the name of the class. Then once I put a dot after the name of the class, these are all the class level members right here. So you can see this method here called get counter. It's a class level, not instance level. And now we can get the number of video games in our collection, like so. If we wish to output that to the console, we can just copy that method here, put it right here, and then delete that semi colon. Now I'm going to run the application. You can see we have a similar result. It's just getting the grand total of the number of the video games in my collection. And I appreciate I've just spelt collection wrong, but nobody's perfect. That is an example of a static method and also a static field in C Sharp. Perhaps this static keyword that we've been seeing in all of our tutorials so far is starting to make sense. Now our main class here is called program. By default, there's a method called main which is static. This main is a class level method. By default it's the first method that gets executed when the program is run. If I create a new method here, for example, I've just created a method just like this. I attempt to call this method from main. This is a static method. This is not a static method. Watch what happens. So you can see there's a red line here. If I hover over that, it says the object reference is required for the non static field or property program test. That's because we're calling a non static method from a static method which is not allowed. If something is not static then it is an instance level method. Because we're inside a static method. Here, there's no instance to operate on, we haven't created an instance, We're not within a method of an instance. There's nothing to do with instances going on here. We're inside a static method, but we're trying to call an instance level method. It's not going to work. In cases like this, you would have to create an instance. This is just an example. Anyway, I wouldn't recommend you create an instance of the program class, but it just helps my explanation here. Once I put the instance before this instance level method, you can see the error has been resolved because anything that's not static should belong to an instance, it's a instance level. What we could also do instead of that is just mock this method as static. That way we're calling a static method test from another static method is perfectly fine. One other thing we can do with the static keyword is to mark an entire class as static. What we do, we take the static keyword and put it next to the class definition right at the top here. When you do this, everything inside the class here must also be static. Because if you define this at class level, then it implies that everything within must be static. This is why all these errors are appearing here. But the main important thing about marking a class's static is that we cannot create instances of static classes. They are abstract and sealed implicitly. If you remember an abstract class, you can't create an instance of it. And if you remember a sealed class, you cannot inherit from it. So this is implicit, this is why we have all these errors here when creating a new instance, so we can no longer do this. Let's take a look at turning this class into a purely static class. Strap in and buckle up. Let's go. All of these private fields must be static. Now our constructor in a static class, it must be static. But static constructors cannot have access modifiers. We cannot have public there. Also, it can't have parameters. Let's remove those two also. This keyword is irrelevant because this is only to do with instances that has to go too. Now, all our methods and properties must also be static, and that should about do it. This is an example of a static class right here. Now you may be wondering, well, if I can't instantiate this class, then how is this constructor even called, for example, what's going on here? Well, by default, when you run the application and access this class, this constructor is executed by the run time environment once. This will get executed automatically one time. Anything in here in the constructor, the static constructor should initialize any variables or anything you want to do. That's the purpose of a static constructor in a static class. Now, if we come over to our main file here, you can see we can't create instances of the static class. We can only access things at class level. Now, I've marked everything as static, The properties, the methods, this is how we pretty much refer to the class. We put the class name like before and then a dot. Then we can access various things here. And now, because there's no instances for this class, all of these members will exist one time because that's the point of static. We can set a publisher and access that. Also, we can get our video game count like we were doing before. It's no problem. Just to prove that the constructor is run once, check out this method here where I get the counter for the number of video games I have. I'm just going to duplicate this method, so it's called twice. I'm going to put two breakpoints on here. The code stops when this line is hit and then going to go inside the constructor and put a break point there. I'm now going to run the application, so you can see what happens. Now the constructor hasn't executed, but the break is on this line here. Video game dot get counter. If I step over this, you can see the constructor here is called. If I step over that, we get the counter, we go to the next line. If I step over that, you can see nothing happens. The constructor is only called once on this first line here, and it's ignored on subsequent calls to any methods that exist at class level. I hope this made sense. It's quite a lot to take in, but this is the point of the static keywords to put pretty much anything you want at class level, the concept of instances in this case are pretty much ignored In that respect. I gave you an example of how static constructors also work. The constructor is called automatically just when you touch any method or member, and then it's ignored for any subsequent calls. After that, I hope this helps you. This is the power of the static keyword in shop. 60. 13-1. The readonly Keyword: In this tutorial, we're going to be looking at the read only keyword in C Sharp. Now what does the read only keyword do? Well, the read only keyword is what's called an immutable data type. What does that mean? It means once you have a value set inside a variable or a field for example, then you cannot modify that value once it's been set. What does all that mean and what other conditions are involved in that process? Let's take a look at a small example. Here I have a class called Dog Dog has a constructor that takes one argument called breed, which is the breed of the dog. Like a terrier or a Chihuahua for example. I have two private fields right here breed and another one representing just a unique ID for every dog we construct. And then I have one public property that gets and also sets the breed of the dog with the knowledge we've gained so far. If we want users to be able to say, get the value of the breed, but not set the value we want to make it read only then. If we have a property like this, for example, that exposes this private field here, then we would simply just remove this set clause right here. When we try to actually put information into the breed, it's not going to letters. So if I go dog breed and then try to give it a value, it doesn't really matter what we put in here. We have an error. If we harver over that, it says it cannot be assigned to, it is read only. That is one example on how to make say, a property read only in C Sharp. But wait. At the start of the tutorial, you talked about fields and variables and things like that. How do I do that using the read only keyword? Well, let's take a look. Let's go back into the dog class. Now what I'm going to do is use the read only keyword. I'm going to undo these changes and put this set clause back in here. So we're now setting the value, but now I'm going to mark this field here as read. Only once I've done that, you can see an error has occurred here. It's not actually letting me use the set clause anymore. If I hover over that, it says a read only field cannot be assigned to, then there's a little condition here, except in a constructor we can assign it inside a constructor like here and except it only setter of the type in which the field is defined or a variable initializer. What does all that mean? It's basically saying when you use the read only keyword, you can define it once. For example, we could define it here and initialize it here. Let's just say every new dog is a Chihuahua, for example. It's no problem at all. We're actually setting it, but we're doing it when we declare it. We declare the variable here, but we're also initializing it that is allowed. The other thing we can also do is set it inside a constructor like inside dog. And we can do this multiple times. As long as it's inside a constructor, it's okay. We can do it 1,000 times if we want to, but we cannot set this inside, for example, this property here. We cannot say, create a brand new method and set it here, for example. This isn't going to work. You see the point here. Even if we access this from outside of our class, I just make this lower case. Now to access the field, you can see it cannot be assigned to accepting a constructor. So that's the power of the read only keyword. And there are a couple of reasons you might want to use these when working with immutable data types like the read only keyword. You want to use these for things that maybe you want to set up one time, but then you'd never want to modify the value of this. This is because, for example, if I generate a unique dog ID, for example, I only do this once, but then I don't want this ID to change because each dog has a unique ID associated with it. If I start changing ID's of dogs, then for example, if we have a bit of software that tracks dogs, you know the dogs that wear the collar. And if the dog gets lost, so they can scan the collar or the microchip. And then it uses the ID from that to reference maybe a database and find out where who the owner of the dog is. Perhaps, don't make this read only then we might have a property or someone calling this application might accidentally change the ID, which could be disastrous. This is why immutable data types are generally used. We want to prevent fellow developers, or even users of the software, from modifying these values. But for something like an ID, where we generate a unique ID for each dog in our system, it's very important that we make fields like these read only. So it really depends entirely on your system what you want to do. But it's really good practice to say, if you have variables or fields which you do not want the users to modify, then always make these read only for example. So that's one way you could handle this problem. Another condition to do with the read only keyword, for example, it can only be used on fields. Now remember, fields are what are defined in classes, just underneath the class declaration. If I go into my A main program here and use it inside a method. If I define this inside a method, obviously removing private, then you can see there's a problem. If I hover over it, it says the modifier read only is not valid for this item. That's basically saying, okay, you cannot use the keyword read only inside a method, but we can use it at class level. For example, we can use it here and it's no problem at all. That will work just fine. But we cannot use this inside methods. There is a different keyword we could perhaps use for that, and that is the constant keyword which we will be talking about as well. The last thing I want to talk about to do with read only is when we can set the value. We can set the value at compile time, which means we can give it a value in our development mode when the software compiles, that's when the check is done. I can give a value to red, here, I can say Chihuahua and there's no problem. This is at compile time. Again, inside the constructor, we're setting this value. However, we can also change the value at run time when the software is run. However, we can also initialize a read only field during run time when our software is actually running. When we construct this dog object right here, the constructor is getting called and then this line of code is executed. And this happens during run time when our software is running. If I run the software, you can see it sets that value in the constructor. There's no errors and it's no problem. We can set a read only field at compile time and at run time, two different places. But that is the read only keyword in C Sharp and why you should use it and also how you can use it. 61. 13-2. The const Keyword: I'm going to be talking about the constant keyword in C sharp. It looks something like this. What is this? Well, the constant keyword is another immutable data type. If you watched my tutorial on the read only keyword, then understanding the constant keyword is going to be a lot easier. In this tutorial, I'm going to be explaining the constant keyword, but also demonstrate the differences between constant and read only as a lot of people get confused between the two and which ones they should use and when. Let's take a look at the constant keyword. Now what I'm going to do is use the previous example. This will help illustrate the difference a lot better. So here I have my dog class for anyone that didn't watch the last tutorial. I have two fields here, a constructor that sets these up and one property right here that just gets the value of the breed. So it's a simple dog class. What I'm going to do is modify this private field here, which is currently read only, and change this into a constant. Then I'm going to demonstrate the behavior and the differences in this case. So remember with a read only field right here, we can actually set the value from a constructor and we can also initialize it. Let me change this into a constant now. Now you can see an error has appeared. If I hover over the error right here, it's saying a Guid type cannot be declared as a constant. Certain data types cannot be constant. That's a bit of a problem. Okay, let's make our ID an integer. Instead, we'll have some system that generates a unique integer for each unique dog. Okay, no problem. We'll use a different data type. Now there's another problem. If I hover over this, you can see a constant field requires a value to be provided. Basically, that means when you declare a constant like we're doing here, you have to initialize it, you have to give it a value all on one line right here. Otherwise, it's not possible. When we declare something as a constant, we have to give it a value. Let's just say 456, for example. Now there's another problem down here. If I haror over that, you can see, well the error message isn't very clear. But basically once you declare a constant and initialize a value into it, you can then no longer modify this field or variable from anywhere else. Not in a constructor. You cannot modify it from a property. You cannot modify this value from outside of the class anywhere else. Once a constant has been set and initialized, which you both have to do on one line, you cannot modify this value. So think of the constant keyword as more like a stronger read only with a lot more limitations in terms of modifying your data. This is a real big difference here for something like generating a unique ID for a dog, read only as a good keyword for this, because we can initialize it from the constructor. However, generating a unique ID for a dog with a constant keyword, this would be a very bad way to handle this situation because const wouldn't be a good way to represent this. You may be asking, well, what can I use const for? What is a good example of using this constant keyword? It seems quite limiting and it seems like I can't really do much with it. Well, for example, let's say we work with I. When I say pie, I don't mean an apple pie. I mean pie R squared 3.1 419. I think pie is accessed in the math static class. We've looked at the math static class before when working with numbers previously. And there's lots of things you can do in here. But you can see in here, there's one called pie. If I hover over that, you can see pie is a constant, 3.1 4159. I was close, I was close. Pie is a constant. And that's because pie doesn't change. Pie is always 3.14 159265. It just is that value. There's no reason that I can ever think of where we would want to modify the value of pi, because pi is what it is. Pi is pi. It's the relationship of the radius to the circumference. Now, I'm not a mathematician, but hopefully I put the point across that you would never need to modify pi because it is a set value. This is a very good example of using a constant. In this case, pi is constant. You don't modify pi. It is what it is. And when you try to, you can see there's a problem here. So pi is a very good example of where you would use a constant, because this value, once set, is never changed and there's lots of them. Look, there's pi there and towel. I've never heard of towel, but oh, it's to do with radiance. Okay. Here, a distant memory of a very early math lesson. So you can see this is the point of using constant. It's where you would never want to change the value. And once it's set, it's set now constant, You set this at compile time, not run time. When your application is running constant, variables or fields need values. You can remove the value, run the application, and assign it while the software is running. This only happens at compile Time. Another thing with constant, unlike read only read only you use it on private fields of classes like we explained previously. However, with Constant we can use these as private fields of the class, but we can also use them inside methods. For example, I can just declare a variable here I call it ID, I give it the value, then I can use it in the remainder of my method right here. I could also pass it to another method, it's no problem. Constant variables, you can set and declare and initialize and then pass them around methods, it's no problem at all. However, if this was read only like we showed previously, it's not possible because read only is restricted to private fields. One other thing I'm going to mention about the constant keyword is that it's implicitly static by default. Basically that means it's static by default. If you watch my previous tutoril where we talked about the static keyword, you'll remember that static is a class level. This is where we create a new instance of dog. Then using the instance which we've created, we can access instance level, fields, methods, properties. But when we access things at class level, we use the name of the class, then access anything at class level. Things at class level are static, Just like the constant here. What I'm going to do, I'm going to make this constant ID public. That means we can access it from outside of the class. I go back outside here, I put a dot. Now you can see the ID is here. This is because fields which are marked as constant are implicitly static, static. If I use DG the instance at instance level, you see the ID is not here. It's not here at all. But at class level, this is where it lives. This is because anything defined as a constant is implicitly static. It's available at class level. You can see it's not static at all, it's just constant. That's because this has a value and wouldn't set. We can't modify it. Why would we want every instance to have a bit of area in memory where this ID is defined? It doesn't really make sense. If you have 1,000 dogs in your system, then some of your memory will have to be available to add this constant ID for each dog in your software. Now, this doesn't make sense because once it's set, it's set, that's it. So it makes sense really to have this available to the class. So if we have 1,000 dog instances in our system, we don't have 1,000 copies of a variable that cannot be modified. So that is the reason for this and it sort of makes sense when you think of it that way. That's really a bit of a gotcha to do with constant fields, is that they're at class level. I hope in this tutorial I've highlighted what the constant keyword does, what it means, and more importantly, the difference between constants and read only in C sharp. 62. 14-1. Stack and Heap Memory: When developing applications with C Sharp and Visual Studio, and you're creating things like variables like integers, boolenes, maybe instances of classes, objects, arrays, and things like that. It's important to understand what is happening with those in the computer's memory. What if I told you this? Depending on what data type you chose for your variables determines where and how this is stored in memory. What do I mean by that? If you use an integer variable or a bolen variable, or a double for example, then these are stored and accessed very differently from different data types. And when I say different data types, I mean things like strings, arrays, and custom objects. But why is that important? Well, there's a couple of reasons why you might want to learn about stack and heap memory. One, for performance, your application can run and function a lot faster when you understand these concepts. But not only that, but what if I told you that, for example, if you pass an object into a method, you could potentially lose data or overwrite existing data. What would you think about that? Now these are two of the many reasons to learn about stack and heap memory, and this is the purpose of this tutorial right now. Now from experience, and believe me, your average developer won't have much knowledge on what's happening in memory with these variables. However, just having a tiny bit of knowledge on this will let you stand out from the rest of them. So let's talk about stack memory for a moment. The architecture of stack memory is kind of like a stack of pizzas or something like that. You keep adding pizzas to the stack, one on top of another, and then remove them sequentially. So the top one first, followed by the next one you can't access, for example, pizzas in random orders. It has to be added to the stack. So added to the stack of pizzas or removed from the top. So this is how stack memory works. It's sequential, so you add things to the top and you remove from the top, we keep short lived items on the stack. Now what is a short lived item? Well, these are generally called value types. Things like integers, Boo leans characters, floats, doubles, things that are kind of quick, simple things which are considered not complex. Simple data types like those, not things like complex objects. And when we store things in stack memory, it's retrieved fast. It's a very fast area of memory, just from the way it's architectured sequentially. Now, the heap area of memory is quite different. Imagine that stack of pizzas, but instead of a nice organized stack, throw them all on the floor, so there's pizzas everywhere in heap memory, there's no ordering of the items in the memory per se. However, because of the natural layout of items in the heap memory retrieval is slower because the process is more complicated on accessing the data. Therefore, it's considered slower than stack memory. Generally, you keep long lived items on the heap, so complex objects, but also things that will be made available for a long time, for a long duration of the running of your application, whereas things on the stack would be considered short lived. So maybe a quick calculation like four plus four, for example, what kinds of data types and items are stored in the heap area of memory? It's things like objects, classes. When we instantiate a class, strings, strings can be huge items, arrays, anything which is global, globally available throughout your whole application. For example, even though a simple integer is considered a value type. However, if you made this global like static or something like that, and it's made available to every class in the system, then this is where the rules change. This would be stored in the heap area of memory because it needs to be made available for longer, so long lived items in the heap. Things like strings, classes, as are all considered reference types, that's the key word. You may hear a lot in the future when you create a new reference type which is stored in the heap area of memory. What also happens is that something called a pointer is created on the stack. So what happens is the pointer on the stack points to an area of the heap memory where your object data lives. When you create a reference type like an array, for example, a pointer is added to the stack and the actual meat of the operation is added to the heap. The piece of information on the stack pretty much says, okay, you can find it right here at this memory location on the heap. That is the only thing that gets added to the stack when you create a reference type, like something complicated, like an array, for example. This is where the name reference type comes from because we're referring from the stack to the heap where the data canner lives. And this is why things like integers, Boulen, shahs, simple types are called value types because the value is directly stored in the stack area of memory. Now I appreciate that this is quite a lot to understand and take in, but don't worry about understanding every single thing I've outlined in this tutorial. The main takeaway is to know and understand that certain data types are stored in the stack area of memory. And the stack area of memory has its own characteristics and benefits, and other data types are stored on the heap, again, with its own characteristics and things like that. In the next couple of tutorials, I'll be using some examples so you can further understand this. So don't worry about understanding everything right now, but right now I'm going to talk about something called a stack overflow. Now, you may have heard of the website stack overflow, or maybe you've heard of the term before. It doesn't really matter if you've heard of it or not, but what we're going to do is intentionally cause a stack overflow in C Sharp. And I think it will be quite a fun example to simulate, because I can show you that stack memory has size limitation. And this is why large complicated objects are stored on the heap. So let's try and overflow the stack area of memory. Now with a quick example. I'm over here in visual studio. Now I have a very simple application from the main method. Here we're calling an overflow method. And the overflow method is just writing hello to the console window. So not much is going on here. Now an easy way to cause a stack overflow is to have a method call itself. You may be asking yourself the following question, how does this cause a stack overflow? I'm not defining any integers, Booleans, anything like that. What is actually overflowing the stack? Well, when you call a method, the method reference is also added to the stack. This is another example of stack memory. So we can achieve a stack overflow like this as well. Similarly, we can create a few million variables, the integers, perhaps that would work too. Maybe there's lots of ways to accomplish this, but this is a quick example of a very easy way to do this. So I'm going to run the application now and we're going to see what happens. I run the application, it pretty much crashes out. It says in visual studio, stack overflow exception. When I look at the console window here, you can see it says stack overflow repeated 24,109 times before the stack is completely full and it started overflowing. If we look at this diagram here, you can see how the stack and heap memory grow, but the stack memory is limited. The point of the stack memory is to store actual values for data types like integers. It'll actually store, for example, 15 on the stack, rather than if we have a big reference type like an array, then this is stored on the heap because these can grow very, very large. However, with the stack area of memory, it's limited. It's finite. You can only put so much information here. And as you can see here, we can store a reference to our method call 24,109 times. So that is how limited it is and this is why everything isn't stored on the stack. Yes, the stack is fast, but its space is limited. The heap is slower, but it's a lot larger. So you see this pros and cons of each, and this is why both of these exist and also why it's important to understand both. So I want to talk about one more thing, and that's the call stack. What is the call stack? If I come back into visual studio here and scroll down, you can see there's a little window here called called stack. If you don't see this window, then come up to the top, go to bug, then windows, and then call stack. And this should appear at the bottom right here. What the call stack does, it gives you a visual representation of your method calls, for example. So you can see here we started with the main method. Here we called overflow, and we repeated this 24,106 times before finally ending in a stack overflow. It gives you a nice visual representation of your method calls. And you can see the architecture here is pretty much like the pizza example I was talking about earlier, with the first call being the bottom pizza. And these are slowly added onto the stack. But the reason I'm talking about the call stack right now is that beginner developers, can I get a little bit confused between stack memory and the call stack? The call stack gives you a nice visual representation of your method calls. But it's not stack memory. This isn't what you see in stack memory. The call stack doesn't show you your variables and assignments and things like that. It only gives you like the method calls while they are loosely related, the call stack is not stack memory. I can illustrate that now with a better example of the call stack. Take a look at this example here. It's quite simple. The main method here calls method one. Method one calls method 22, calls 33 calls four. Finally, in four, we just say hello to the console window. It's very simple, but this example will show you how the call stack works and how these method references get added into stack memory. Basically, the stack architecture, the pizza architecture. Let's have a look at an example. Right now, I've added a break point here on the very first line. So we're going to enter break mode as soon as this is hit. So I'm going to compile and run the application now, now we're in break mode here. If I just bring this window up with the call stack, you can see one item has been added to the call stack which is main. Now I'm going to step into this by pressing 11 on the keyboard. Now you can see I'm inside method one. Now this has been added to the call stack here. This is our first pizza in our stack. This is our second pizza. Now, I'm going to press F 11 again. Now we have our third pizza on top. I'm going to step into this again. We have our fourth pizza. You can see how this works. So the call stack gives you a nice visual representation of where you are in your application during a debugging session. It's semi interactive as well. You can double click these and you can see where you are, where this method was called from, which is really helpful when you have multiple files, solutions, projects, things like that. It can navigate you directly to where this was called from. But this is a similar representation to how stack memory works. We have our first value here, then they get stacked on, and then they get popped off in order like this. They cannot be accessed at random. So it's like first in, first out, which is the terminology there, stack memory and the call stack use the stack architecture. And while they're related, they're not exactly the same thing. I hope that makes sense. Now if I then go to method four, you can see that's the last one added onto the call stack. And then I step over that, and now you can see they're slowly getting popped off the stack. The method three will be the next one to pop off because we're just coming out of there. Then two, then one. Now we're back in the main method. You can see it's the last item remaining in the call stack. So that's what the core stack is, and that's also what stack architecture is. And you'll see stack architecture in many different programming languages, but it's not limited to programming either. One last thing I'm going to talk about is a key word you may hear in the future called garbage collection. So what is garbage collection? Well, when I talked about creating reference types, for example, things that are stored in the heap area of memory, like classes, instances of classes, strings, arrays, and things like that. I also said that a pointer is created on the stack and this points to the information on the heap. It's like a pointer. What can happen is the pointer is removed from the stack area of memory, but the actual data is left behind on the heap. Now, our application has no idea where this information is anymore. Maybe it doesn't even need the data anymore. But it could still exist in the heap area of memory. But because the pointer is no longer pointing to it in the stack area of memory, this data on the heap is useless. It can't be used, it can't be found. It can just fill up your memory until there's no memory left. This is quite a big problem. This is usually referred to as a memory leak. So there's something called garbage collection that actually kind of goes through the heap. Area of memory, works out if there's a pointer pointing to it on the stack, and if not, it removes, it frees up the memory. And this is what garbage collection does. And in a language like C shop, you don't have to worry about garbage collection. But I thought it'd be an interesting bit of trivia to tell you. But if you work with other languages, perhaps like C plus plus, then you do need to worry about garbage collection. So maybe it's something to consider, but it is nice to know. And when your application closes or terminates, then generally the memory is freed up. 63. 14-2. Method Parameters - Passing by Value: Before watching this tutorial, I highly recommend you watch the previous tutorial on stack and heap memory. Otherwise, this might not make a whole bunch of sense unless you're familiar with stack and heap memory. Now let's take a look at this example. Here we're looking at some method passing now passing some parameters into a method. Then we're going to modify some values. Just consider this example here. It's quite simple. In the main method of the application here, I'm defining two value type variables here. Now these are stored in the stack, the stack area of memory, they're value types. Then I'm outputting the values for these variables to the console window. I'm then calling a method called reset. And I'm passing both of these value type variables into this method right here, I'm resetting these variables which are being passed into zero and then I'm outputting them to the console window. Once the method is finished, executing control is passed back up here. And then I'm outputting the values of these variables again. And then I'm keeping the console window open. Question, what do you think the output would be? Well, let's take a look at what the output actually is. I'm going to run the program now. The value of num one is the value of num two is four. And then the value inside the method is zero because we're resetting them. And then after the method is run 6.4 is that what you expected? Perhaps so, but now look at this other example. Let's take a look at this example here. It's very similar to the previous example, but instead of using a simple value type like an integer, we're using a reference type. And reference types, like we talked about before, are stored in the heap area of the memory, and a pointer to that data is stored on the stack. What we're doing, we're instantiating a video game object. If I go to the video game class, you can see it's quite simple. It has one private field here called title and one public property called title, which controls getting and setting of this field here. Very simple. We're setting the title for the video game here, a World of Warcraft, and then we're outputting it to the window. We're getting the title before a method is called. Now we're changing the title here. In this method, it takes in a video game object and then we're outputting something to the window. We're outputting it to the window inside the method. But before we change the title of the game inside this method, we're changing the game title to change something different. Then after the method is finished executing, we're outputting the game title again. Now what do you think will happen this time? Okay, let's take a look at the result. If I run the application, you can see here the game title before the method is World of Warcraft. The game title inside the method is World of Warcraft. Remember inside the method, this is before the change has taken place, but after the method has finished executing, we come back to Maine and output this. Here however, you can see it's retaining the value which we changed it to inside the method. Why is this? Why are these changes being persisted from changes inside methods for reference types but not value types? What is going on here? Well, allow me to explain. I'm coming back to the previous example now where we had two simple value types here, two integers, and we passed them into a method here. Now in C Sharp, when passing objects, whether they're value types or reference types as parameters to methods, by default, these are passed as value. They are passed by value, unless explicitly noted, they should be passed by reference. We're going to talk about passing by reference later. But consider the default which is getting passed by value here. What does passing by value mean? Well, by default, when you call a method and pass in these two parameters here, a copy, a copy of this data is created. Here we have a value of six in number one and a value of four in number two. We're calling this method here. Inside this method, it receives a copy of these variables. It's not pointing to the same area as memory of these. These are literally copied. Then the method actually works with a duplicate copy of these variables. This is what it means when being passed by value. Any work we do inside this method here is done with a copy of these variables. And when the method has finished executing and control is returned here, we lose everything inside here because this is a duplicate copy and it only exists within the method. Once the method is finished, we have no knowledge of this unless we specifically return something out of here. That is an example of passing a value type into a method and it's being passed by value, it doesn't affect anything outside of the method. Coming back to our other example here where we changed the name of the video game object. If I'm passing data by value, then why is this change persisting outside of the method? Surely this doesn't make sense. Well, this is because we're passing a reference type by value. Like I said, when you pass parameters to methods by default it's by value. However, we're passing a reference type. Remember before we talked about reference types, which are complicated objects. They can be arrays, lists, all things like that. And this is stored in the heap area of the memory, but like I said, there's a pointer which is stored in the stack area of memory which points to this data in the heap. When this method is called, yes, it is copied to the method, but the heap memory is not copied. Only the pointer on the stack is copied. Now this seems counter intuitive really because, yes, we're passing this reference object by value. However, because it's a reference object, we're only merely copying the pointer inside this method. Here we're working with a copy of the pointer which is stored in stack memory. However, it still points to the same area of memory on the heap. In this main method, we're pointing to the area of memory on the heap, but also inside this method. Even though we're working with a copy of the pointer on the stack, it's still pointing to that area of memory on the heap. This is why the title still changes because even though we're working with a copy of the pointer, it still points to that same area of memory. This is why the title still changes inside the method. And we can see here, once the method has been called, the changes still persisted after the method's execution. In here, I appreciate this is quite a lot to take in, but if you look at the previous tutorial and also this one a couple more times, you will understand it and you will get it, I promise when I said a copy of the pointer is passed into this method here, for example, if I now work with this copy of the pointer. So this game here, I can initialize a new object, a new instance. What that does, it allocates a new area of memory. Here, I'm working with the copy of the pointer right here, but I'm saying, okay, now create a new object on this copy of the pointer. So what this is going to do, this is going to work with entirely new copy of the data and put this on the heap. What we're doing here, once the method has been called, we're outputting the game's title here. In fact, let's put this here. Now we have a new instance of game. We're setting the title of this new instance to changed, and then we're outputting it. And we're still outputting the title after the method here. What do you think will happen now? Well, let's take a look. Let's run the program. You can see now something slightly different has happened. We have our original title at the start here. Then inside the method, it's been changed. However, after the method now it still retained its original title from before. Why is this what is going on here? Like I mentioned, this is a reference type. By default, it gets passed by value inside the method. We have a copy of this reference types pointer, which is in stack memory. We're now giving it a new memory location and setting that new location to change. However, outside of the method, this has no knowledge of this new memory location. This is only inside the method that this is happening. Only inside this method has the knowledge of this new area of memory on the heap and that we're pointing to it. However, this change is not persisted outside of the method rather than working with an existing copy of the pointer, which again, will affect the heap. Just like out of here, we're actually allocating a new memory area on the heap and pointing our copy of the pointer to that, and that is why this happens. Let's take a look at one more example here. Again, this is going to have pretty much the same output as our previous reference type, which was an instance of a video game object. But here we have another reference type, a list. Again, it could be any reference type, It could be an array, it could be a dictionary, it could be many different things. This, again, is stored in heap memory. A list with four integers, we're outputting the count of the list, and then we're passing the list to this method. Now, by default it's passed as value, but this is a reference type. A copy of the pointer is copied to the method. Now the method can work with a copy of the pointer which points conveniently to the same area on heap memory as this one. Outside the method. We're then adding two numbers to the list, then outputting the list count. Once the method is ended, we're outputting the list count again. What do you think the results will be? Well, let's take a look. You can see the counts of 466. That's because the method is adding two numbers. And once we're out here, it is pointing to the same area of heap memory, it's going to retain that count. Now in the method, if I just modify the list slightly here. Now inside the method, this list is being passed again as value. But it's a copy of the pointer. With the copy of the pointer and now pointing it to a brand new area of heap memory, and then adding two numbers to this brand new list. What do you think the output will be? Now let's run the program. You can see we have four to four. You can see our initial list has four. That's correct. Inside the method, we're creating a brand new list. It only has two numbers inside. That's where the two comes from. Now the method is finished, we still have access to this original area. In heap memory, it's outputting the four. So you can see it works with all different types of reference types. And this is default behavior of methods in C Sharp. So I'm going to come full circle now. At the start of the previous tutorial, I said, why do I need to know about stack and heap memory? Why is it important? Well, you can see if you don't have any knowledge of stack and heap memory and value type variables and reference type variables, then unexpected things can happen. Unexpected things are quite a big problem in software for obvious reasons. This is why it's important, and here's an example of this in practice. 64. 14-3. Method Parameters - Passing by Reference (The ref Keyword): The ref, key word passing method parameters by reference. If you haven't watched my previous two tutorials on this subject where we talked about stack and heap memory but also passing by value, then I highly recommend you watch these before proceeding with this tutorial as they tie into the concepts outlined in this tutorial. In the previous tutorial, we talked about how various different object types when being passed as parameters into methods. By default, they're passed by value, that meaning a copy of the actual value or a copy of the pointer is created and the method works with the copy. Now I'm going to talk about passing by reference. Now, passing by reference is not default behavior and it includes talking about a brand new keyword called the ref keyword. So how does this work? Just as a little refresher here, we're setting up two integers, outputting their values. Then inside this method, we're passing them in as parameters, resetting the values to zero, outputting the variables again. Then when the method is done, we're outputting the value of the original variables. And you can see we're passing these by value. The method only works with a copy of them. Therefore, the data is never changed once the method has finished completing. Now what I'm going to do is change this slightly. I'm going to pass these value types. Remember value type is integer, boolean, simple types stored on the stack. Now I'm going to pass these by reference. To pass something by reference, you just prefix the variables here with the ref keyword in the method parameters. Here we do the same thing, we just add the ref keyword. Now what do you think the output will be? Well, let's take a look. So you can see it's exhibiting the behavior of the reference type from the previous tutorial. Remember when we modified the value of a reference type and it remembered it after the method had been called? Well, this is what's called passing a value type by reference. And we can do this by adding the F keyword here. What is the advantage of this? Well, passing a value type inside a method, it doesn't create a copy of the value anymore, so no copy is being created. It's pretty much saying, okay, hey method. I'm going to pass you these two variables here, they're value types, but I want you to pass you the reference to them in memory. I want you to work with these. And anything you do to them, the changes will be reflected. So this is passing a reference to the area in stack memory for these value types, and now they're being passed as reference. We can work with these directly inside the method, and any changes we make to these will be persisted once the method is finished executing. So you can see here I've just changed them, now the change has been persisted. So you can see now we understand the default behavior in the last tutorial which is passing by value. It's easier to understand the other terminology which is being passed by reference, and that is using the Ref keyword. Okay, we've looked at passing value types like integers by value. We've looked at passing reference types like complicated objects by value. We've now looked at passing value types by reference. And now to complete the quadrilogy, we're going to look at passing reference types by reference. Here's the example. Here we have our list of integers that we looked at before. We just have four numbers in there. And then inside this method, we're adding two numbers to the list. And then outside, we're just outputting the count of the list along the way. We looked at this before and you can see here's the output here, because by default we're passing a copy of the pointer, but it points to the same area in heap memory. So you can see the changes being persisted once this method has finished executing. But remember when we talked about the fact we can actually set up a new location in heap memory and take a copy of our pointer and give it a whole new location, and that changes the result. You can see here the change is not persisted in this case. Now I'm going to qualify this with the ref keyword. I add that here when we call the method. And I add that here in the parameters here. What do you think is going to happen now? Well, let's take a look. I'm going to run the application. You can see now the change has actually been persisted once the method has finished executing. Why is this what's going on here? Well, you may have already guessed it. When we pass something by reference using the reference keyword, just like we talked about before, no longer creating a copy, we're not even creating a copy of the pointer anymore. We're pretty much passing the pointer in stack memory to this data in heap memory. We're passing the pointer itself to the method. The method is now working directly with the original pointer to this information. Now we're setting up a brand new object here, a new list. But we're not working with a copy of the pointer, it's the original pointer. We're pretty much just creating a brand new list over the top of the original one and then adding two numbers to it. If we run the application now, just like we saw previously, you can see here it's being persisted. That's the difference here. When using the ref keyword, we're no longer copying anything. We're not copying the value types, but we're also not copying the pointers when using reference types. Why is this useful? Well, then our methods can work with our original data, whether they're value types or reference types, and the changes can be persisted once the method has finished executing. That's the power of the ref keyword in shop. This completes this three tutorial series on stack, heap memory, and reference and value types in C shop. 65. 15. The struct Keyword: In this tutorial, I'm going to be talking about structures in C. Sharp structures use the keyword struct, but what are they and how do they work? Well, structures are very similar to classes, and this tutorial assumes you know a little about how classes work, how inheritance work, perhaps interfaces and also value and reference type variables and also the read only keyword. I've done tutorials on all of those previously. If you've watched everything so far, you'll have a full understanding of this tutorial and you're going to hit the ground running. What is a structure? Let's take a look at this example. Right here I have a square class, let's take a look at that now. It has two private fields here, the width and the height of the square. It has a constructor which sets up those fields. It has a sample method here that just calculates the area based on those. And also two public properties here that expose the width and the height. So it's quite simple. So what I'm doing here, I'm instantiating a new object, and I'm outputting some sample things to the window. If I run the application now, a square with height four and width five has an area of 20. So it doesn't really do all that much. So let me introduce a structure now and what it is. So this go over to the square class here. And I'm just going to modify this class keyword and I'm going to put structure like that. So if you watch my tutorial on interfaces and enumerations where we create a brand new class and just modify the class keyword. It's quite similar in that regard. And now we have a structure. This square is now a structure. It's no longer a class. But you can see there's no errors here. There's no red squiggly lines. How is it I've just modified this whole entire class and there's no errors. Does the application even run? Well, it looks like it runs. And we have exactly the same answer, what is going on here? Now this is where structures and classes confuse new developers or developers that don't really have an understanding of value types and reference types. Structures and classes can seem very similar in how they behave. You can see here, I've made a structure, It has private fields, it has a constructor, it has methods, properties. What is the difference here between a structure and a class? Can I just use structures now instead of classes or shall I ignore structures completely and only use classes? Well, the answer is you can use both. One of the main differences between structures and classes is that structures are value types. Now, how does that work? Well, we talked previously that classes are reference types. If I put this back here, square is now a class. I just uncomment this method here. Now this method here, I'm passing in the square, which is now a class, into this method. And I'm modifying some properties here. I talked about this previously. When you pass a reference type like this one here, this is a reference type, it lives in the heap area of memory to a method, then it's passed by reference. That means the method can access the memory on the heap. It works with the original object when the method is finished. Here we still have access to the changes made from with inside this method if I run this application, now we're going to see these changes reflected in the output here. Let's take a look at that. You can see here 2,020.400 for the area. It's a reference type variable right here. It lives on the heap. Now let's change this back into a structure and see what happens. Now this is a structure I mentioned previously. The structures are value types and not reference types. These changes will not be reflected in the output. That's because the method works with a copy of the value type. Anything changed in here, it's just reflected on the copy. The changes will not persist. We're going to see 5.4 like we did previously. As you can see there, that is one of the main differences between classes and structures is that classes are reference types and structures are value types. That's one main feature of structures. Let's take a look at some other differences between structures and classes, as they are quite similar and they seem to operate the same. Let's talk about the differences. I think that will let you better understand about what structures can do, the advantages and also the disadvantages. With structures, we cannot use inheritance classes, for example, we can inherit from a base class. But when we try to do that with structures, and we hover over this, it's shape in interface list is not an interface. What does that mean? Quite cryptic, isn't it? That's because with structures you can actually implement interfaces. You can work with interfaces, It's no problem. This error here, it's expecting an interface because that's pretty much the only thing in that regard that you can do with a structure. But when I try to inherit from a class, a base class, it doesn't let me do that because it's not possible. The whole concept of inheritance does not exist with structures. That's one advantage a class would have over a structure. We cannot inherit from a base class, but the structure itself also cannot be an abstract class or a base class. And that means we can't have virtual methods, for example. You can see here when I tried to do that, it's not even valid, it's because it's inside a structure. So we can't use the keyword virtual, which means we can't override, which means we cannot do any polymorphic behavior. And remember, that's the concept of method overriding. For example, we can't use virtual, we can't use abstract. So we can't pretty much use anything with regards to inheritance or anything like that. With structures, there are a lot more simpler types than classes, so think of it that way. A structure is more simple than a class. Let's talk about maybe an advantage of a structure here, or maybe why we would even use one. Why even bother? Why don't we just use classes for everything? Well, structures don't have a heavy memory footprint like a reference type object would. For example, I have a video game object right here, video game class. Inside here it has private fields linking to other reference types like a game class, a list of integers, some strings, an enumeration. This is quite a heavy footprint and this lives on the heap. For that reason, we don't put it on the stack. But if you use, for example, a structure for a very simple class, for example this square class right here, It only has simple value types like just some doubles. Even if it had Booleans and integers, things like that, it's going to operate a lot quicker than allocations and allocations on the heap. So when working in the stack area of memory with simple value types and even structures, then it's going to operate a lot quicker. And allocations, again, are a lot speedier and cheaper as well. So this is an advantage of using a structure. So you may think, okay, what if I have a reference type inside a value type? For example, a list of integers is a reference type variable. And then I go ahead and put this inside my structure, which is a value type. Yes, it's possible. You can see there's no errors. The application is going to run, but this is considered bad practice. You should not do this. This kind of defeats the point of using a structure in the first place, which brings me back to my next point. Only use a structure if you have a container for simple value types. For example, this square here. It has a width which is a double. It has a height which is a double. If it has a color, maybe you could represent this by an integer. And that integer might reference something to do with a color. For example, white might be zero, Black might be one, Red might be two. These are working with simple value types. Here, a structure in this instance would be perfect because it itself is a value type. But I'm also using value types within. I never plan on using inheritance, I never plan on using polymorphism. I never plan on other structures or things inheriting from this. Therefore, a structure would be a good choice for this. It's simple, it's quick, it uses value types. I never want to expand on it to do with inheritance. If all those boxes are checked, use a structure. But as soon as we start thinking things like, okay, I think this square should inherit from a base class shape. And maybe the color could be an enumeration, maybe it would have a list of pixels and things like that. And we start introducing inheritance and heavy and reference type fields here, then no, we don't want a structure, we want to use a class. So basically in a nutshell, use a struct if you have a cheap object, but use a class if you want to expand it and use heavy reference type objects. That's basically the difference and why you should use one and not the other. So one of the main advantages at has over being a value type and everything to do with that is that you can mark the entire structure as read only. Now if you watch my tutorials on Read Only, you'll understand what it does. It's an immutable data type. Once you've set a value, you cannot change it. And there's lots of reasons for that. If I try to mark this entire class as read only I haror over this you can say it's not valid for this item. But if I make a read only structure like this for example, then there's no problem at all. Obviously, there are a couple issues to do with that. So you can see instance fields of read only structure must be read only. These do need to be read only as well. The other thing, of course, we can't use the set modifier if things are read only. We have to either initialize in the field declaration here, so we initialize here or within the constructor here. If you watch my Tuchoil on read only, you will remember that and understand that, but I thought I'd just mention it again. With structures, you can mark the entire structure as read only. Which you cannot really do on a class using this keyword. And you'll see maybe moving forward with your programming ventures, you'll see this is quite common practice as well when working with structures. This is one powerful thing you can also do when working with structures. But I think the main takeaway from this is don't be afraid to use structures and experiment, but only use them for simple containers. So things like squares where you have simple value types. As soon as you start talking about heavy loaded reference types, then in that case, use a class. But structures are very good for working with like quick muck up applications or simple things like these. I hope this tutorial helped you. 66. 16-1. The object Data Type - Boxing and Unboxing: In this tutorial, we're going to talk about the object data type. And it looks something like this. You may have encountered the object data type when writing to the console. For example, when we write to the console, there's lots of different method overloads we can use here. But you can see one of the parameters here is object for example. What is that? How does it work? Well, let's take a look at what the object data type is. If you watched my tutorials on inheritance and also value types and reference types, then understanding the object data type will be quite easy for you. Now, the object type is the ultimate base class for all data types, all types user defined, Whether we create instances of objects, reference types like arrays and things like that, and also simple value types like integers, bolenes, characters, and things like that. It's the ultimate base class for all of these types. It's a reference type which means it's stored in the heap area of memory. Also, it's like an older technology. Now something came along called generics. And generally, generics is a better practice, although you do still encounter the object data type these days. And using the object data type can present some issues and problems which we will also talk about. This is the process of boxing and unboxing. Let's take a look at an example now, when I just said that the object data type is the ultimate base type, what does that mean? Remember before when I talked about interfaces and we can pass the interface around into methods, then when we implement the interface, then we can pass our objects around. If we have multiple classes extending the same interface, we can just pass those objects around freely. This is pretty much similar to how the object based class works. Don't worry if you didn't watch those tutorials on abstract classes and interfaces. I'm going to explain it right now. Here, we're just calling a method and we're passing a string. It just says hello world. The parameter is a string. Which is great because we're passing a string and then we're outputting it to the window. A very simple application. Now imagine this. I'm going to change this string to the object keyword, just like that. Now let's run the application. Again, you can see we have exactly the same result. Why is this happening? Well, it's simply because a string like this one here satisfies, that is a relationship. And it is an object just like an instance of a class. For example, a video game class, a dog class, an animal class. There are also classes, but they are also objects. This object keyword here can represent pretty much any data type in the system. Bouls, strings, and even integers. For example, 3456. The output will be the same, and there's no problems with compiling the project. Here we have an integer here, 3456, we talked about it before. Simple integers, strings, characters, boolenes, they're all value types. They live on the stack, in the stack area of memory. However, objects, they're reference types, these are stored on the heap. What happens here, there's an implicit conversion happening here. This integer that we're passing in is being converted into an object type. This process is called boxing. If we then convert this object value back into an integer, then this is called unboxing. If you don't believe me, I'll prove it to you. Now if you work with an object type like value here, it offers a few methods that we can use, one of them being called get type. What that will do, it will get the underlying type of this object value here. Right now we're passing an integer in here. If I run the program, you can see it's outputting the underlying type of the object, which is an int 32, a 32 bit integer. Similarly, if I pass in a string, say hello, then we're going to get a string for example. You can see this is the underlying type of the object right here, and we can get that using the get type method here. Let's talk about boxing and unboxing right now. Let's first talk about boxing. What is boxing? We have an integer here called numb, and we're initializing it to 1234. Now what we're doing is putting this integer into a box, hence the name boxing. We're basically saying, okay, I want to create a brand new object. Remember this is the ultimate base class for all types. I want to give this the value of num. Now OBJ should equal 1234. Now I want to change the value of this num here to 100. Do you think this value will change with it? What I'm doing, I'm outputting two of the values right here. If we run the application, the value of num is 100, which is true because we changed it. But you can see this is not reflected to our object value right here. What is going on here? I thought object was a reference type. When something is a reference type, we have a reference to that area of memory. Well, this is the penalty of boxing. What happens here when you box something, you're pretty much putting this integer inside an object box. But because object is a reference type, all objects are stored in the heap area of memory. Simple value types like integers are stored on the stack. What happens here when we're creating a new object and we're setting it to numb, here, we're pretty much copying this whole entire object, allocating some extra memory on the heap area of memory, putting that value in there. And then also creating the pointer on the stack to point to it. A lot of things are happening when you do this here. Now this is implicit, which means it happens automatically behind the scenes. You don't have control over this. Boxing, a very expensive operation when we looked at our example before where we passed an integer into the method and we had a parameter of object. All of this happens behind the scenes. A whole area of memory on the heap is allocated just because we're passing an integer and it gets implicitly converted to an object type. This is the penalty of boxing. It's also something we should consider very strongly, especially when creating large scale applications. Is there a better way of doing this? Maybe you should consider of overloading the method instead. Like when we have console right line, we have all these different method headers here. We can take in a char array, a decimal, a double afloat. But once we have all these possible values yes, then there is an option to take in an object. But it's not mandatory. There are design things to consider when using objects here, like this way, when you box certain data types, we could box a string, we could box a character, but in principle, this process is called boxing. Now, the opposite of that, as you may have guessed, is unboxing. What is unboxing? Well, unboxing is pretty much the opposite. And that's converting a reference type, like object stored on the heap, remember the heap area of memory back into a value type, then stored in the stack. This is the opposite of boxing, and that's unboxing. It's doing the process in reverse. Let's take a look at an example of unboxing now. Now I'm going to unbox this object here. Remember, the process of unboxing is converting a reference type into a value type. Let's take a look at that. Now, I want to convert it back into an integer. If I convert it to a different type, then there's going to be an error. We're going to have a type conversion issue. I want an integer out of this whole operation. That's the point I'm on boxing the object back into its original type. I set up an integer called result. Now what I want to do is convert the object to the expected data type. This is the expected type I want, this is the conversion. I want to convert this object to an integer. And this is the process of unboxing objects stored on the heap. I want to convert it to a simple data type, and now it's going to live on the stack right here. This result integer here. Now if I output the result to the console window, let's have a look at the result. You can see how I have my original value here, 1234. Now perhaps you notice one thing about this tutorial, and that is, hey, I'm introducing this object keyword here, this object data type, but you shouldn't really use it that much. Yes, I appreciate that's the general theme of this tutorial, but it's good to be aware of this. In the early days of C Sharp, it was quite common to convert various data types this way. So we convert it to a reference type and back into a value type. And that allows us to pass different data types as the ultimate kind of base class object. So it was quite useful, but then things like generics and other things were introduced which kind of pushed this whole object notation of boxing and boxing out of practice and out of fashion. But it is something to be aware of, namely because perhaps you might be working with older systems or you might be working with systems that tie in with yours. Like it's called interoperability, where your software links with another piece of software and you will encounter this object data type. As you can see, it's still in use today. Console right line takes an object as a parameter and many other methods and classes also use it. But it's good to know the principle of the object data type and the expensive process of boxing and unboxing, which is implicitly converting data types, value types to reference types and then back again to value types. So there's quite a big overhead with boxing and unboxing in C sharp. 67. 16-2. The dynamic keyword and Dynamic Type Checking: In this tutorial, we're going to be looking at the dynamic keyword. And the dynamic keyword looks something like this. But before we talk about the dynamic keyword, let's just step back a few steps. If you watch my previous tutorials where I talked about C Sharp, the fact it's a strongly typed and also a statically typed language. So let me just talk about that for a second. A statically typed language is where the variable types, for example, an integer for example, is known at compile time. That's when I click this little green play button right here. The software compiles. And if there's any problems, the compiler will alert me, the software won't compile. And this is a statically typed language like C sharp. This process is called static type checking. Static type checking, however, what if I told you that there was also something called dynamic type checking? What is dynamic type checking? This is where the variable types, for example, are known at run time. If there's a problem with the types or anything like that, we can compile the software just fine. However, if there's an error, we won't know until the software is actually running. What do I mean by all of this? Well, let's take a look at an example here. Here I have a sample integer. I'm initializing it to the value of 55. Then I'm just outputting it to the screen. It's not really doing much. However, what if I want to maybe now assign a string value into this integer? If I just type hello, for example, you can see there's an obvious error here. It cannot implicitly convert the string to an int. That's because the type of this variable is an integer. But what we're trying to do here is stuff a string into it. It's not going to letters. Not only that, but our program will not compile. You can see there's an error here. This is an example of the static type checking. It knows it's an integer, so it's an integer type. But now we're trying to put a string in there. But we're actually alerted to this problem right now in development. So this is known as static type checking. However, with something like dynamic type checking, then you won't be alerted to this error. Everything will look fine, the software will compile just fine. But unless you do something about this particular error here, you will be alerted about this error during run time. So, there are other programming languages out there, for example Python or Ruby. Now, these are dynamically typed languages. That means, for example, we can do this and the software will compile just fine, it's no problem. However, you will be alerted about this error during run time while the software is running. This is called runtime and this is where the error may present itself at compile time. This is where C Sharp can catch these potential errors to do with types, and that's called statically type checking. However, at run time in languages like Python, Ruby, then you'll be alerted about these type errors. For example, during run time, and that is called dynamic type checking. Now I've talked about static type checking and dynamic type checking and the differences. It's going to be easier to explain the dynamic keyword now. So under the hood, the dynamic keyword behaves pretty much like the object data type. If you watched my previous tutorials where I talked about the object data type and it's canal considered to be the base class for all of the types, for example the base class of double integer bolen. But not only that, but things like lists and custom objects and things like that. So if you remember and understand that detail about the object data type, then you're going to hit the ground running with regards to the dynamic keyword. Now let's take a look at an example. So what I'm going to do now is do an example with the object data type. So this variable here called test, is going to be a type object. What I'm doing is storing a value here, 35.5 which could be a double. For example, it looks like a double to me, but there's no problem here because object is like a base class here, it's going to accept that value just fine. But now we're trying to increment this value of test, which is data type object by 7.5 It looks like we're adding a to a double. Which should be fine when we had it as double before. It worked with no problems. So you can see here, there's no problem. But now I've turned this into an object data type, there is a problem. So if I highlight this, it says operator plus cannot be applied to object and double when working with object, we talked about boxing and unboxing. What I'm doing here, I have a simple data type here, 35.5 which is like a double, and I'm stuffing this into an object data type. Now if you remember from before, this is a reference type, so it's stored in the heat area of memory. What we're doing is boxing the value here into test. When we try and increment the value, there's a problem here. We can't add 7.5 to this value here. What we have to do here when incrementing the value, for example, is explicitly convert this object data type to a type we can work with. What we're trying to do is add 7.5 which is a double, so I have to convert this to a double. We can convert it to a double using the convert static class that we've been using all along in the previous tutorials. And that's going to work just fine. What I'm doing here is unboxing the value here. I'm boxing here, I'm unboxing. There's a bit of a performance payload here when we do the boxing and unboxing like we talked about before. But it works just fine converting the object to a double. Then I'm adding a double to it, then I'm storing the value back into the object, so I'm re boxing it again and then I'm outputting the value. If I run the program, now you see I have the value 43, which looks about right. You can see it works. No problem. I can actually add values together. I can even add five here, for example, and it's going to work just fine. This is a bit of an advantage of using something like this over individual data types, But there is a performance cost. But the point I'm trying to make is when you use the object data type and you wish to modify the values, you need to do this unboxing here. You have to do an explicit conversion here. Now, with the dynamic keyword I'm about to introduce, I said it's very closely tied to the object data type. It behaves very similarly. But we don't need to do this explicit conversion right here. And that's not the only difference. One of the main difference is that it provides dynamic type checking in a C Sharp environment. So let's get started with the dynamic keyword. So the very first thing I'm going to do, so you understand it a little better, is to convert this example using the dynamic keyword. So what I do here, I define this variable as dynamic here. And because it's not the object data type, and we don't need to explicitly cast anything, we don't need that cast right there. So if I run the program now you can see it's working just like before. It's not complaining about adding a value to an object data type. So you can see there's a considerable advantage right here. We don't need to explicitly cast our variables, for example. So that's pretty good. And like I mentioned before, it works like the object under the hood. So it's almost like, you know, the master base class that works with integers, bouleenes and all things like that. So that's the first advantage of using dynamic. We don't need to explicitly cast anything, so we don't need to explicitly say, okay, make this an integer. So therefore we can now add an integer to it or make this a double. So we can add a double to it. We don't need to do any of that. It looks perfectly fine. Looks, so we've defined it as a double, now we're adding an integer to it. All of the conversion casting boxing and done boxing is done behind the scenes. We don't have any visibility of that. It's all done for us. So that's one advantage of this, that complexity is taken away from us. Watch what Als can also do. For example, we initialize, this is like a double, and then we want to add an integer to it. Now, what if I say test equals hello, for example? What do you think will happen? Now let's run the application, what it looks like, we're outputting hello. So what I'm going to do, I'm going to add some breakpoints here. We're going to enter break mode when we run the application. And then we're going to analyze this variable test down here. So let's bring this up so we can have a better look. Right now, you can see we have a dynamic object right here, which is test. And it doesn't have a value yet because we haven't executed this line of code. Once I step over that, we can see that test is now, because we've put a double value into it, now we're incrementing the value by five, which seems pretty fine. So you can see it's still a double. Now, trying to put a string value into here, if we step over this, you can see now we have a dynamic string here. So you can see it's quite flexible in the way it works. It pretty much just throws out the whole concept of types or at least hides the concept of variable types from you. So while developing applications, it may feel like all that complexity is taken away from you. You don't need to worry about is it a string, is it an integer. Perhaps Python programmers, or if you've done some Java script, you might find this really useful. But however, errors can occur during run time, and this is when your application is actually running. So there are a few problems associated with the dynamic keyword that you have to be careful with. So the dynamic keyword, it probably sounds quite great to you. We don't have to worry about types, we don't have to convert to different types. We can just use it for everything. You know, why not? And maybe there's a slight performance here, but otherwise it seems pretty good, right? Well, let's talk about the downside of using dynamic right now. But first I'm going to introduce an example where we work with some custom objects. So what I have here, I have a video game class, it's quite simple. It has four private fields, a constructor, a sample method, and just a sample public property right here that just gets the video game title. It doesn't do much. I've instantiated the class. Here I have a video game object called Game One. If you've followed my 00 tutorials from before, when we make use of this instance. Here we can see various things. We can see our get publisher method. And we can see our property right here, the title. We can see this when this window pops up here, this is like Visual Studio helping us. And another word of that is called Intellisense. And what Intel sense does, it just gives us some nice autocomplete features. It saves us from typing. For example, we can double click to this and then we have access to the method number one. We know the method is there. Number two, we know we can access the method, it's not private or anything like that. Number three, if we double click it, we don't have to worry about typos spell checking, so it's quite good. It also gives us parameter types we can use and also lets us know about return types. So Intel sense, otherwise known as visual studio, helping us is a very good feature and I highly recommend using it. However, when using the dynamic keyword, Intellisense is not available. Now, there is a good reason for this, but it is one of the big disadvantages over using the dynamic keyword. Let's take a look at that now. Right now, I'm just setting up a game here. Then I want to get the publisher, for example, let's just store that in a string. I'll store it in a string called Pub. And then I just want to output it to the window. Not much is going on here. It should output Blizzard, for example. Let's run the software now, and we can see Blizzard. It looks like it's working just fine. Now let's turn this into a dynamic type. Now I have a dynamic object called Game One. It has the value of the new instance of the video game class. Like I said, it doesn't have to be a double an integer. It could be a complex type, it could be an array, a list, or even a custom class, like the video game class. Absolutely, no problem doing that at all. Fully supported by the dynamic keyword, And again, this is like the object behind the scenes. Everything is fine so far. And if I run the application, we get exactly the same result, no problem at all. But watch what happens. Now I put a dot after game one. You can see we've lost all of that in tally sense. Visual Studio is now refusing to help us. We don't know what methods we have available unless we actually, you know, kind of look at this and maybe copy and paste them in. However, it has a lot of problems this way. The thing is, it relies on Earth not to make mistakes. Number one, like I said before, maybe this is a private method, so we can't even access it outside of this class. So therefore, you know, we could create a whole big problem here. So if I run the application, now it's saying it's inaccessible due to its protection level. Well, what if I made a typo? What if I put F here? You can see it's not highlighting it red. Run the application and it doesn't contain a definition. Well, that's because I spelt it wrong and it's an accident. But I don't have visual studio helping me. I have zero Intellisense. So this is one of the downsides of using the dynamic keyword. You have absolutely no intellisense at all. And intellisense is really useful, and a lot of people take it for granted. But it gives you all the methods and properties that you can actually use on an object. So you may be wondering what was that sorcery before where you misspelt publisher and there was no red line? Why was that? What's going on here? Why was the program able to run you? That's normally not allowed. Well, yeah, that's true because if I turn this back into a video game object, you can see we get the red line. And that's because at the start of this video, I said that C Sharp was a statically typed language. And that just means everything is caught at compile time. So I can't even compile the application because this is where the errors are caught. However, when using the dynamic keyword, then all of this is gone away. Nothing which is dynamic is caught at compile time. So the error is gone away. The program can compile. The program compiles when the black window pops up, as you can see there. But now the error is actually caught at run time. And this is the error that gets thrown. It's called a run time binder exception, right here. So run time binder exception. So this happens at run time while your software is actually running. So in a nutshell, when you use the dynamic keyword like this, visual studio just gives you free rein. It literally says, okay, do whatever you want. If something's dynamic, call any message you want, call any property you want. You know, it doesn't matter. I'm going to give you no red lines. I'm going to let you compile your software, you can do whatever you want to do. You can introduce human error, pretty much You have free reign. So that's an advantage, or perhaps a huge disadvantage, of using the dynamic keyword. So the choice is yours in that regard. But programming languages like Python, Ruby, even Java Script, these are dynamically typed languages. However, C Sharp is a statically typed language. So you may be wondering, well, why does a statically typed language support this in the first place? You know, why do we even have this? I thought this was a statically typed language. Well, what if you want to create software that works with Python software? For example, if Python and Ruby are dynamically typed languages, then maybe my software needs to work with them. And a fancy way of saying this is called interoperability, or interrupt for short. If I want to create software that works with someone else's software, but they used a different language, then this is where the dynamic keyword is actually quite useful even working with the document object model. Now this is something HTML and XML use when using things like that. You just do not know what methods and properties are available until run time. This is why it's quite useful. Not everything is known at compiler time. When your software compiles, sometimes it's only made available to you at run time. So this is why the dynamic keyword is really useful. So a couple of fancy bits of terminology for you. If we have our simple video game object like we talked about before and we wish to say, call a method called get publisher, then this is an example of what's called early binding. And that just means, okay, this method is available to us, we're using it right here. Any errors will be caught at compile time. When we click this little gray button and the binding is done early, everything works, There's no error. For example, if I did this, then there's an error example of early binding. However, if this was dynamic and we try to do this right now, we have no idea if this method is available. We have no idea if this method is public, private, internal protected. We have no idea if I spelled it correctly. However, when I run the application, then the binding is done during run time. Right now, okay? Yes, the method is available. We've just called it, we've got a result. This is an example of late binding, Early binding before late binding during run time. A couple of things you may hear in the future, but I thought I'd bring them up now. One other thing I didn't mention was dynamic. If you define a variable, for example a simple integer or something like that, whatever you really want, the type isn't important. You don't need to initialize it. You can if you want to. There's no harm in doing that, but it's not required. You don't need to say, okay, this equals five. You can work this out later on. That's another thing you can do with the dynamic keyword. One other thing you can do with dynamic is even pass it into methods and return it out of methods. I've just set up a sample method called Echo. It's just going to echo the value of the publisher. For example, I know for a fact game one publisher which will get that for me, I have no Intellisense. I assume it's spelled correctly. Then we're just going to output that to the screen. Let's comment that one out and then we'll call the actual method. This looks pretty good. We're passing the game object in which is dynamic as a parameter to the method and echoing the result of the get publisher method. Let's run the program. It looks like it's working. You can see here, but not only like I mentioned, we can return the dynamic keyword as well. So here I'm calling the method here that now takes no parameters. I'm initializing a new video game object, and I'm instantly returning it. But I'm returning the dynamic keyword because I don't want a video game object. And then I'm catching the result here in a new dynamic game object, and then I'm getting the publisher. So you can see equally it works as a return as well, dynamic. You can pass around no problem at all. So let's summarize the dynamic keyword right now. The dynamic keyword, we don't have to worry about the types, we don't have to worry about casting types. All the boxing and boxing conversion is done for us. That's great. However, there's a performance impact. Again, we have to worry about spelling our methods correctly working out if they're actually accessible. Lots of different things. In a nutshell, dynamic isn't used in a typical C Sharp application. If you're just making a calculator or something quite simple, you shouldn't really use the dynamic keyword. However, if you're working with perhaps other pieces of software which have been developed in dynamic languages, or maybe something called a com object or the document object model for HTML. This is where the dynamic keyword shines and this is where you should use it, because in instances like that you don't have access to these methods at compile time anyway. You may only have access to them at run time. So this is where you would use the dynamic keyword in this sense. So it's not used in common shop applications. So it's one of those with scenarios where you never really ask yourself, should I use the dynamic keyword. It's usually presented to you. Okay, yes, this definitely looks like I should use the dynamic keyword. And that is what generally happens when you're architecturing a new piece of software, for example. So the dynamic keyword, it offers dynamic type checking, and it's basically the object data type, but on steroids. Thank you for watching. I hope it was useful. 68. 16-3. The var Keyword and Type Inference: Based on everything we've learned so far. What if I told you that we no longer need data types? For example, we don't need a video game object data type. We don't need a list data type. We don't need a string array data type, not even an Interble or a character. And everything's fine and the software will compile. What the hell is going on here? Well, let me introduce something completely different. Now in this tutorial I'm going to be talking about the Varki word in C sharp. It looks something like this. If you haven't watched my previous tutorials on the dynamic keyword where I talked about dynamic type checking and also static type checking, all that good stuff, then I highly recommend you watch those before proceeding with this tutorial. Otherwise, you're going to have a harder time understanding the concepts highlighted in this tutorial. So what is the Var keyword? How does it work? Well, we can use the Var keyword when defining something like a variable. For example, we have an integer variable here and we set it to 55. We could equally set this as a v, what looks like a Var data type. However, Va is not a data type. The keyword Var is shorthand for okay. Figure out what data type this actually is when you compile your application, for example. So all checks using the Var keyword are done at compile time. Now remember in our last tutorial where we talked about the dynamic keyword and how everything to do with a dynamic keyword was figured out at run time. For example, do the methods exist? Do the properties exist? And then it kind of links it together in a late binding. At run time, well, the Va is done at compile time. So for example, if I try and call a method on a var variable, for example, then it's going to error if the method doesn't exist. But we're going to cover that later. Let's take a look at a small example using the var keyword and then we'll go from there. Let's take a look at a couple simple examples right now. Here I have a local variable here called test. But rather than giving it, say, an integer or a string or something like that, I'm using the var keyword here. And as I mentioned before, it's up to Visual Studio and the compiler to work out what data type this is. I say Visual Studio because I've just defined the variable here. And if I hover over it right here, you can see it thinks it's an integer. If I change this to a string, it doesn't really matter what's in there. It can be empty. I hover over test, and now it's a string data type. What it does, it works out the data type based on what you initialize it to. I've initialized it to a string. Here you can see when I hover over it, it's a string data type, just like before. It could be an integer or even a double, for example, now it's a double. Now when I actually compile the application, this is where it works out if anything is valid or invalid based on what you've done. This is the compile process and this is where it actually figures out what data type it is it compile time. That's a simple example there on how Var is not a data type. But you can see it actually bases its data type on what you initialize it to. What happens if I don't initialize? Well, that's not possible. You can't actually define something with the var keyword and not give it a value because then the system cannot work out a data type from this whenever using the var keyword always must initialize it from that it can work out what data type it is, for example, a string. The process of working out the data type based on the initialization value, well, there's a fancy word for that and it's called type inference. You may hear that in the future. It's called type inference, and that's where we guess the data type based on the initial value here. Now our local variable here, the type, is a string because this is based on the initialization value here. What we cannot then do is then just convert this to a totally different type. You can see here. Cannot convert type into string once this is initialized. For example, this is now a string. It's pretty much a string for its lifetime. We can't just then, okay, make it an integer, make it a booling. We cannot do that with the Var keyword. Let's take a look at an example with some more complicated objects. Now for example, let's define a game object. This is our video game class where we just pass in some sample values. Here, you can take a look at the class here. There's not much going on. Private field, a constructor and a sample method. What I'm going to do is just call this sample method here called get publisher back out here. I'm setting up a new video game object, but I'm storing this in a game right here, which uses the Var keyword. So now using this game object, you can see I have full Intellisense here I have the full visual studio help. Unlike the dynamic keyword, because remember in the last tutorial when I talked about dynamic, everything is figured out at run time. So we have no Intellisense at all, because all of this is figured out at compile time. Then I have full access to the Intellisense. So I'm not going to make typos, guessing methods, calling methods that are perhaps private and I'm calling them outside of the current class. I'm not going to make those mistakes like perhaps would using the dynamic keyword. So if I run the application, now you can see I'm getting the publisher no problem, and I have full access to the Intellisense available. So let's talk about a few pitfalls of using the Var keyword. What can't I do with it? And why is it bad? For example? Well, unlike the dynamic keyword, Var doesn't really have that much disadvantage or much negative impact. However, there are a few disadvantages. For example, we cannot use the var keyword with methods. So here I have a test method here. If I try to return something of var type, it's not going to let me. Similarly, if I use it as a parameter and just give it a name, again, it's not going to let me either. This is just simply because visual studio doesn't have enough information available to guess the type based on a return or a parameter. Or at least that's what I'm led to believe. But you cannot use the var keyword as a parameter to a method, or even return a v from a method. It's just not possible. But with the dynamic keyword for instance, you are able to, you cannot with the var keyword. Let's take a look at one more potential disadvantage of using the Var keyword. Now let's clean up some of this stuff here. What I'm going to do, say for example, I want to create some financial software. I want it to calculate money, but I want a high degree of decimal accuracy. I don't want to lose money due to my software of not allowing enough decimal places. It's quite easy to do. In an instance like this, I need a decimal data type. If you remember my early tutorial where I talked about decimals, I talked about floats and I talked about doubles. If you remember, decimal has the highest degree of accuracy, so lots of decimal places. Doubles are somewhere in the middle. And floats have the least precision, the least number of decimal places. I want a decimal because I'm working with money, I don't want anything to get lost. I'm going to create a new variable. It's going to be using the var keyword and I'm going to call it money. Now, I'm going to initialize this. May it doesn't really matter what value for example, but I'm going to put maybe something like this. Actually, no, let's just make it zero. So I've initialized it as zero and now if I harver over this, you can see it's assumed the data type is double. Now double is like a medium degree of accuracy, but there's no error. You know, there's nothing wrong with this syntactically. It's perfect. The application runs. I'm outputting zero right here. Now the system doesn't know my intention, the system doesn't know. I want to create an application based on money. I actually want a high degree of decimal places. I want this to be a decimal behind the scenes. So how do I do that? Well, when defining a decimal, you need to just put m right there. And if I harver over money, you can see it's now a decimal, not a double. But you can see that's just human error. I could easily forget to write that m and now I have a double. So maybe if I compile my software, give it to my clients, they start using it for example. Then they notice that a little bit of money is missing due to rounding because this is assumed to be a double. So I'm losing a lot of degree of accuracy by making that tiny mistake. This software is responsible for losing money, and that is not good. And again, you might not be losing money. You could be gaining money, but the fact is it's wrong. So I could easily forget to use this M here and get a decimal. So it is something you should be really careful with doing. So I'll just highlight this to you now if I just set this money value to a high degree of decimal accuracy, because we're working with money, when I run the application, you can see all of this accuracy has been truncated, so quite a lot of information is missing. And that's just for the fact of using an m right here. So, you know, it's quite easy to do. Whereas if I were to find this as a decimal to begin with. And then I do something like this, then you can see there's a red line, so the software won't even compile. There's an error. And it's pretty much saying, okay, if you need a decimal you have to use the M suffix here. I'm never making that mistake. If I explicitly define this variable money as a decimal data type, That is one particular scenario where using a Var keyword could create problems. In the future, I want to show another example now to do with the Var keyword and a potential disadvantage of using it. Here I have my video game class right here. It has some various fields in here. What I'm going to do, I'm just going to copy these fields and move them into the main method right here so I can illustrate something. What I have, I have these various types here. I have integers, strings, list of integers, and also a game object as well. What I'm going to do, rather than have these data types here, I'm going to replace them all with the Var keyword. And you'll notice something when I change game info to use the Var keyword, now we have to give it a value before we could just leave it like this. What's called null, It has no value, and we'll talk about null in a later tutorial. But now it actually needs a value because it needs to work out the data type from when you instantiate the object. So now we can't leave this empty like this. We need to give it a value. That is one important thing to note. When using the var keyword, we have to initialize it. What I'm going to do, I'm just going to change these into the Var keyword. So we can see one more thing as well. Now, the other disadvantage, maybe potential disadvantage, or at least awareness is that when looking at declared variables here, it's hard to tell what data type these are. Maybe we can figure out console is a string and title is a string, et cetera. But we can see the zero and know it's an integer. But using this, especially anywhere else in the application, we would have to hover over the variable each time and work out that it's an integer by looking at this name alone. Obviously, there's var next to it, so we don't see the int datatype either. It's a little unclear at a first glance what data type this is. Perhaps we can be more careful with our variable names and maybe call it rating int, or perhaps rating number. And then we know from a first glance that, okay, it's a number. It's especially useful when debugging, but it is just something to note when using the var keyword, especially declaring the variables. Here, this kind of explicit information with regards to the data type has disappeared. We can really only have the initial value to look at. We have to hover our mouse over each one just to get clarity on what data type it is. So when you have large, complicated pieces of software, and you're trying to debug, you know, hundreds of variables, it can be quite time consuming to work out, you know, what type the variable is, and maybe there's a type issue. Maybe you're trying to feed a string into an integer, for example. If that's a potential bug, then it can take, you know, a little longer to work it out when we don't have explicit types here. And we're kind of having to hover our mouse over each one to work out what the type is. And by no means it's a deal breaker, it just forces you into a good habit of naming your variables correctly. For example, a variable called rating number could be a better name than just rating. It gives a bit more information about the data you're storing in this variable. If anything, it teaches you to be a better developer. The last thing I want to talk about is when should I use the Var keyword? Should I ignore it completely and just retain it as a bit of knowledge or shall I use it all the time? Are there any downfalls? Are there any practical reasons? Well, a lot of people actually use the Var keyword for everything. I've looked at software and they don't even use data types, or at least hardly ever everything has the Var keyword. I mean, there's nothing really wrong with that, especially if you use descriptive variable types. You're quite cautious about when you define decimals and floats, for example. So there's nothing really wrong with using the Var keyword. You can use the Var keyword for pretty much everything, or you can use standard data types. It's up to you. But there are a couple situations where the Var keyword does have a few advantages. So let me show you those now. So let's clear out some of this example here. Let's say for example, we're creating a piece of software that manages a bunch of video game stores. We have our video game class here. Each store that sells video games will have a list of video games in their collection. It will look something like this. However, we want to manage multiple stores. Each store will have a list of video games, but perhaps we want to catalog what every single store has. In a situation like this, we would have a list of a list of video games. And that will be like the Ultimate Game Collection, for example. So in this case, look at this data type here. It's quite long, it's quite annoying to write, it's quite complicated to look at even. You could even expand that by saying, I have a list of a list of a list. So you know the kind of predicament goes on. You can see how big that is. But in a situation like this, you could use the var keyword. And that just simplifies all of that. It saves a lot of typing. And you can see you have a nice handy shortcut there in cases where you have quite large data types here and you don't want to type it all out and for whatever reason, in tell sense isn't offering it up to you. Or maybe you want to loop over it and you don't want to write out this whole data type. It's quite easy just to use the Var keyword. You know, it's no problem at all. And, you know, in cases like this you're not defining decimals or doubles and there's a risk of maybe losing decimal precision, then something like this is perfectly fine. It's quite an easy way to do it. And you can see how quickly it was to type just three characters on the keyboard versus all of this here. Just one example there, there's a couple more examples as well, which we haven't yet covered, but we're going to cover one of them. So one of the two examples is something called link queries. And another example is creating anonymous objects, which we will be talking about soon. And the var keyword is very good for creating anonymous objects. But to summarize, and the takeaway from this tutorial is var is not a data type. Var is just a nice way of saying, okay, let's figure out the data type based on the initialization. And this process is called type inference. So this is the var keyword in C sharp. 69. 16-4. Anonymous Types: In this tutorial, I'm going to be talking about anonymous types in C shop. If you haven't watched my tutorial on the Var keyword, then I highly recommend you watch that first before watching this tutorial. So anonymous types, what are they? Let's take a look at an example here. Here I have a class called video game, and I'm creating four objects. It doesn't really matter what's in here, but there's a constructor, some fields, various properties and things like that. So you can see in this example, I'm setting up four objects here by prefixing them with our classes like a data type. Then I'm instantiating a new object with all these parameters. But in order to do this, I have to create a class. Now, my class has to have a constructor. Well, it doesn't have to have one, but I do have one and I do want one. It has all these private fields, some methods, and properties and things like that. So it has all of that stuff in this class here, just in order to create for objects right here. But with something called anonymous types, we don't have to define a class. You see this class here where we define video game. We don't need any of this definition. We don't need this file. We don't need this class per se. So how does that work? Why would it benefit us to not have a class but we need to instantiate from the class? That doesn't make sense to me. Please explain anonymous types, they're useful for a couple of reasons. One of the primary reasons is something called Link. Now, we haven't talked about Link, so I won't talk about that now. But another situation, for example, say you're prototyping a piece of software. You want to do a quick piece of software to make sure something works. Or maybe you don't want to create a whole class with lots of methods and things. Because what you're creating is something quite simple and quick. So there's a couple reasons really. But one of the benefits is speed, and another benefit is if you're not creating something particularly complicated, maybe it only has two properties and you're not doing much with it. Then you can use what's called anonymous types. So how do I create an instance of a class that doesn't exist? Well, that's a very good question. And it starts with the var keyword. So what I'm going to do, I'm going to simulate this video game object here, but rather than using the video game class, I'm going to use an anonymous type. So there's delete all of those and we're just going to use this one as an example. How can I instantiate a class that doesn't exist using anonymous types? Well, because the class doesn't exist, therefore it's anonymous, we can't really start it with a class name here. This is where we use the var keyword that we've talked about in a previous tutorial. Now we want to give it a name, I'm just going to call it game on. Now we need to instantiate a new anonymous object. How do we do that? We use the new keyword, but now we use curly braces. Now inside these curly braces, we're going to set up our properties for our class. This line here pretty much mimics this line here. The only difference is that we don't have to define a class. This class doesn't have to exist. We can call these whatever we would like. It doesn't matter because it's an anonymous type. If I use my object here, if I put a dot right here, you can see I can access all of the properties that I've defined here. I've spelled them using crazy characters like Gampd, but you can see that that appears in the list and I can actually access this as a property. Right here we have a console here, publisher and rating, you can see it doesn't matter what I call them, it doesn't matter what values I give. This is purely anonymous because it has no name, it has no class. Because it's anonymous, we store it using the var keyword into an object. Right here, you can see this is quite powerful. We don't need a class, it's completely anonymous, and to do that we just use the new keyword here. But there are a couple of exceptions with this. When we create an anonymous type like this one right here, we can only create read only properties. There's no constructor, there's no methods, there's no private fields. Imagine if this class here called video game was an anonymous object, then the only thing you can have in here are read only properties, title, for example, publisher rating, and their read only. You can only get the values, you can only set them once. And that is when you define the anonymous type, right here, the anonymous object, but behind the scenes, this is what would be generated when you create an anonymous type. So read only properties, no constructors, no fields, no methods. So they're the limitations of using something like this. It doesn't really stop there. When creating anonymous types. Here what we can actually do is put an anonymous type within another anonymous type. We can create an array of anonymous types. So lots of different things we can do with them. Let me show you an example right now. In this example, I have an anonymous type right here inside another anonymous type. If I use my animal type here and go to dot, I can go to species which is also an anonymous type and access the noise that the animal might make. The species could be a dog, in which the name of the animal would be a dog, and then the noise would be a bar. For example, you can see I actually have cascading anonymous types. They are quite powerful in which they work. And you can see just like using the Var keyword like before, you have full control over the Intel sense. You can clearly see everything you specified in here. That's pretty cool. One thing you shouldn't really do, but you can do is pass these anonymous types to methods. Let's take a look at an example. Now, when I talked about the var keyword before, you can't have var as a parameter for a method, it doesn't work. What you would need is the dynamic keyword in which this would work. If I then call the test method here, I pass in our animal right here. And then we can access it from within here. But because we're using dynamic, if you watch my tutorial dynamic, we have no access to the Intell sense here, but we can use it. However, again, we shouldn't really use dynamic when we don't need to. It's really only recommended to use it when you absolutely have to. I don't see much situation where you may be passing an anonymous type to a method. Really, they should just be used within the methods, they're defined. But if you do need to do that, then yes you can make use of the dynamic keyword in order to get around that problem. So you can see now I'm using dynamic. I don't have access to the Intel sense, but I now can pass this into this method here. So let's check and see if it works. So you can see here outputting bark, It looks like it works quite well. This is an example of anonymous types in C shop because it's an anonymous type and it has no type. Therefore, that's when you would use the Var keyword. And you can see here you can pass it two methods, but you would have to use the dynamic keyword in order to pass it. But I do not recommend doing that. Lastly, when creating anonymous types, these are properties only, and once defined, they're considered read only. And you cannot modify them, as you can see right here, those are anonymous types in C shop. 70. 17-1. The null Keyword: In this tutorial, we're going to be talking about the null keyword. The null keyword looks something like this. What is the null keyword and how is it used also? Why should we use it? If you watched my previous tutorial when we talked about stack and heap memory, and reference types and value types, then you're going to understand this tutorial very quickly. Here are some reference type objects here, like lists, strings, arrays, video game object for example. It's a custom class. All of these are reference types, and they're stored in the heap, which is the heap area of memory. To contrast that, these are simple value types, so integers, boolings and characters for example. Now, have you ever wondered when you declare a variable, so we're not initializing it, we're not giving them values? You can see the software compiles, it works, It's no problem. We've declared them, everything looks pretty good. But have you ever thought about what the default values for these might be? If we don't actually give them a value, what would the default value be? Would it be zero? Would it be, what would it be? Well, let's take a look. I'm going to add a break point at the end of here, and then I'm going to look in the locals window. Let's run the application. Now if we come down here to the locals tab right here, we can view various things to do with our variables that we've just defined. Here you can see our reference types. We have our list here, we have our custom object here, our string array right here, you'll notice something. The current value is no. But if you look at these value types like the integer, the Boolean and the character, or their default values are slightly different. Typically a value type will have a default value of zero. If you represent Bolen as zero, then it would be false. A boolen as a one would be true. You can see Bolen also has a default value of zero. Even this character variable here has a default value of zero. You can see a pattern here. It looks like reference types have a default value of null or whatever null is value types have a default value of what looks like zero. In this example here, what is going on here? Remember when we talked about reference types? When we have a reference type, a pointer on the stack is created. But the actual meat of the operation, the data lives in the heap. The pointer on the stack points to the data on the heap. Now we've declared a reference type here. For example, this list and its default value is null. Now what null is saying here is it's a null reference. We have our pointer on the call stack. This is in the stack area of memory, but we don't yet have anything on the heap, we haven't instantiated it. That means using the new keyword. When we instantiate something using the new keyword, we're creating something in the heap area of memory. This part we're creating the pointer on the stack. This part we're actually creating the data on the heap and therefore the pointer points to it. However, we're not instantiating anything right now. We have our pointer on the stack, but it's not pointing anywhere. There's no reference to the data in heap memory. Therefore, the default value is null, which stands for a null reference. It doesn't go anywhere. However, as soon as we use the new keyword, then the value will change from null and it will point to the data on the heap. Think of null as like nothingness or a null pointer or a null reference. It doesn't really go anywhere, but maybe later on it will. For example, you can see here, this only applies to reference type objects, complicated objects like we talked about before. It doesn't apply to value type objects. However, there is a bit of a condition there. It does apply to value type objects if they're marked as nullable. Now, we're going to talk about nullable later. Don't worry about that. But for the purpose of this example, null applies when declaring reference type objects because we need a pointer, but we don't have one. The initial value is null, which is nothing. Let's take a look at a couple of examples now working with the null keyword. So what I'm going to do, I'm going to output a property, or maybe try and use one of these methods here of these reference types. I'm just going to write to the console window, I'm going to output a random property of this list. For example, I'm going to say list dot count. Let's take a look at what's happening here. Now I have a red line. You can see use of unassigned local variable list. It's not even letting me use this object because it's unassigned. But wait, I thought it was null by default. Well, null by default happens at run time, not at compile time. This is compile time. We're actually doing the development right here. This is compile time. It's not even letting me compile the application. What we have to do at compile time, it's just initialize this to null. That way the error goes away and we can actually run the program. But the compiler is helping us out here. It's saying, look, this is null. You shouldn't really be using properties on a null value, otherwise it's going to fall over. But by tricking it, we've made that error go away. So I can show you an example of using something which is null. Now, list is null. I'm trying to access a property here called count on the null object list. Let's see what happens. Now an error has popped up here and it says null reference, exception object reference, not set to an instance of an object. Now you'll see this error a lot in your ventures moving forward with C Sharp. It's just one of those things. But basically you can see here, our reference type is null. If something is null, we cannot use methods on it. We can't use properties on it because it has no value, it has no memory stored on the heap. It's pretty much just an empty pointer of an object. There's nothing there. It's null, we cannot use it. All we have to do is instantiate it and actually give it something. Now if I run the application, you can see here the error has gone away because we've instantiated the object and it's no longer null. That's something to be very cautious on when working with null. I think you get the point of null. Now, for example, if I have a string, let's delete some of this stuff here. If I have a string, I'm going to call it test. I'm going to initialize it to an empty string. And what I'm trying to say is an empty string, for example, is not the same as null. We've talked about null. We know it's a null reference. What a lot of people do, they get a bit confused with null. They think it's just an empty value, like an empty string. This is not true at all. And I can prove that to you if I just set up a bolen for example. And I have a condition that compares this empty string right here to the null value, and you will see that it's false. What I'm saying here is if test is equal to null, if an empty string is the same as null, I can even write it like this, I don't even need a variable. Then print the value of true if it's the same, otherwise false if it's not. So you can see there, null is not an empty string. A beginner's mistake, perhaps thinking that. But I thought, I'd mentioned that null is not the same as an empty string. Null is simply a null reference. An empty string is just that, an empty string. I hope this clears up what null is and how it's can a used and why it appears. In our day to day lives doing software development. Thank you for watching. 71. 17-2. Nullable Value Types: In this tutorial, we're going to be talking about nullable types. What are nullable types? In our last tutorial, I highly recommend you watch that. Where we talked about the keyword null, I briefly mentioned that reference type objects like lists and objects and things, if you don't initialize them, they get the default value of null, which is a null pointer. However, for value types, these tend to have the default value of zero. But if we try to use the keyword null with a value type object, it's not going to work because we can't really give it a reference pointer. Because it's a value type, it stores a value like 3,456 for example, or true. It actually stores the value of a value type in the stack area of memory. So what is a nullable type? Well, a nullable value type like these is an instance where a value type can actually store null. So why would we want to do that and how do we do that? So for example, when I tried to set this as null before, it didn't work. However, if I add a question mark after the data type right here, you can see that error has gone away, It's been resolved. What is going on here? Well, to turn a value type object like an into ball, a character, simple types. If we add a question mark to the end right here, then this represents a nullable value type. Now this variable is a nullable value type. Now it can take a value, or it can take the keyword null. Why might you want to do this? What is the point of this? Well, imagine you have, for example, a class register. You have a bit of software and it marks the attendance for students in your classroom. Now let's say it has a database attached inside the database, you have all the names of the students, First name, last name, all of that good stuff. And then you have a Boolean in the database and the value in the database would be called something like is in attendance. Now, if the children haven't even arrived to the classroom yet, then we don't know if they're in attendance. We can't really say true because we don't know. We haven't actually done the register, we haven't actually checked to see which students showed up to the class. But if I store the value of falls in the database by default, then I can just change this to true if they are present in the class. Well, I mean, this is saying they're not in attendance, but really I'm not sure yet because they haven't arrived to the classroom. In cases like this, you might want a third value for a Bolen for example. You might want null if we don't know yet. If the student arrives and they're here, we can say true. But if the student is absent, maybe they're sick, we can say false. So in cases like this, we might want a third value. And a key word like null represents something like a default value, like not knowing the outcome yet, or something like that. So if we're not sure if they're here yet, then we could use something like a nullable data type here, which is the Bullen. And we don't know if they're in the class, so we can just initialize it to null. And in the database for this maybe this field would be empty. Or it might even say null. It doesn't matter. But the point is, when the children start arriving into the class, then we can set this to true and false. And that's kind of the principle behind it. It gives you a third option, for example. And again, this is similar with integers. We can set those to null if we don't have a specific value for whatever number we want to model. So anything like that, there's lots of different reasons why we might want a nullable value type when working with nullable value types by just adding a little question mark after the type right here. It does give you a few more options. And why is that? Well, let's take this variable here, for instance. This is nullable. Now, if I put a dot afterwards, I have access to a couple of properties here. If I remove that question mark, so I have a simple bolen, you can see those properties have disappeared. What is going on here? Why do I have these extra properties for a nullable value type? That's because behind the scenes it's a structure very similar to a class. Rather than having a simple boolene like before, where we can just have a boolen and then use it. We can output it to the window, we can pass it to a method, all that good stuff. We have a structure. Think of it like a class. What the class does in this case, it just exposes two properties. One is the actual value for our nullable data type. This now is in attendance stop value would be the same as having a non nullable data type and using that we can use the value property here to get the underlying value which would be true or false. For example, it has one other thing as well called has value. Now we can actually use this Boolean property here to work out if it has a value. What you would normally do for something like this is have an if statement and say, okay, does it have a value? Okay, It does have a value, therefore we can access the value and print it to the console, for example. So something like this and doing things this way and having these properties available to us avoids things like null reference exceptions or just even checking for null for example. This is why it has these properties available. We want to check it has a value and then we can utilize the value. This is why these are quite useful. And this is why when you define a nullable data type, it exposes these extra properties for you to make use of, because it gives you this third option which is null. If you were wondering if you have a nullable value type object and you don't initialize it, then the default value would be null, not zero in this case. Because it's nullable, the default value is null in a nutshell. That is an example of nullable types in C shop. 72. 17-3. The null-coalescing Operators: Null coalescing operators in C sharp sound super complicated. But what are they? Well, one of them looks like this, two question marks, another one looks like this, two question marks followed by n equals. But what are these random characters you're typing? I hear you ask, Allow me to explain null coalescing operators allow you to work with reference types like this list here, for example. Which could be null but it might not be null. Also, nullable value types which could be null or they might be something completely different. Let's take a look at an example here. So here I'm creating a list of strings here, and this is called shopping list. And this is going to contain all the items on my shopping list. So I'm going shopping next, I have this type here, which is an integer and this is the cost of my shopping. Now, I'm going to default this to null because I haven't been shopping yet. Now I may find the time to go shopping, but I may not find the time to go shopping. If I do go shopping, then the cost will represent the value of my shop. However, if I can't be bothered to go shopping, then it's going to retain the value of null because I haven't been shopping yet. Therefore, there's no cost for my shop. Later on in the application, whether I went shopping or whether I didn't go shopping, that doesn't really matter. But I want to output a message that says my shopping cost was then the value of the shop. In a normal world with a simple data type like this, you perhaps initialize it to zero and then, or it could have another value. For example, I run the program, it tells me the cost of my shop. However, if I create a nullable value type like this and initialize it to null, then I typically use the value property to access the value here. However, if this doesn't have a value, perhaps I didn't find time to go shopping, then if I run the program, I have an error here. We've talked about this before. The nullable object must have a value. You can see I'm accessing this value property, but I'm not actually checking to make sure it has a value. What I typically do in this case is just have an if statement here and check the has value property of this nullable type right here. Now I'm saying if I have a value, then I want to output the value. This looks like it should work. Now it looks like I have nothing. But it's not crashing. At least it looks pretty good. But you can see every time I try to access this value, I'm having to do a condition here. I'm having to do an if statement and actually check that there's a value there before I can finally use it. Whether I want to output it to the window, whether I want to pass the value to a method, or a method of a class or somewhere else. So basically I have to check it before I actually use it. But what if I told you there's a way where I can combine these two things into one? Now this is where I introduce one of the null coalescing operators, which is the two question marks. Let's take a look on how I can simplify this here. I'm going to remove the has value check there, and then I'm going to remove dot value here. Then I'm going to introduce one of the null coalescing operators, which is two question marks. I'm just going to use zero as an example here, and I'm going to put parenthesis around the whole thing so it doesn't throw an error. What do you think this is going to do now? Or perhaps you don't know, because I haven't explained it enough. Let's run the software and actually see what happens. I run the software now, it says the shopping cost was zero. You can see, well, the cost is null, but for whatever reason, it's outputting this zero here. However, if I change the cost of 4567 and run the application, now it's actually outputting 4567. What is going on here? Well, this null coalescing operator basically says, if this is null, so there's no value, then evaluate whatever is on the right hand side of these two question marks. However, if this has a value, anything that's not null. For example, evaluate this side of the question marks and ignore this side completely. Don't even evaluate this side. So this is how one of the no coalescing operators works. And you can see we don't need that condition there. It's wrapped up in a tidy little two character statement right here, which is two question marks. So let me illustrate that a little better, just in case you didn't get it the first time. So let me create a method here. And I'm just going to call it get default cost. So what this method is going to do, it's going to return a default value for the cost if no value is specified. It's just going to return zero with this operator here. I'm just appending a string to the result of whatever this evaluates that. It's either going to evaluate to the left side, which is cost, or the right side which is zero. However, it doesn't just need to be a zero or a simple variable. It could be the result of an entire method, for example. Now if this is null, which it is, it's going to evaluate whatever is on this side. It could be a simple type, it could be a method. You see there's lots of options here. It's called evaluating. If I run the application, now it's outputting zero. And just to prove that it's actually running the method, let's run it. Again, you can see the right side is being evaluated because the left side is null. That's the power of the two question marks here, otherwise known as a null coalescing operator. Here is the syntax here, the two question marks here. The usage is, you have a nullable type, whether it's a nullable simple data type, or it could even be a list, for example, because reference types can be null, as you can see there. And then on the right hand side, we have something to evaluate if the nullable type, which is this on the left hand side, is null. We've talked about all of this, but this is a nice visualization if you didn't get it the first time. This is one of the null coalescing operators Right here. I want to introduce one more null coalescing operator now that looks something like this. It's two question marks followed by an equal sign. And it's quite similar to the last example, but it's to do with assignment as well. So what does all that mean? Well, let's take a look at this example here. I have a list of integers here. And this list will total all of these expenditures. So all of the bills I paid this month, all of the cost of the shopping I've done this month, and the whole entire cost of spending my money on useless things. So all of these will get added to these totals here as separate line items. It's a list, so I want to add each of these totals to this list. So we can do that quite easily. We can make use of the ad method that adds this to the list, and then we can just put the totals here, but remember, it's a nullable type, so we need to use the value here, which looks fine, but oh, wait, no. Now we have to check, it has a value. We have to make use of this property. Oh, yes. But that has to go in a condition here to make sure it has a value. For example, then we can add the value in. This should work, but remember when I said null coalescing operators are shortcuts for all of this. We don't need all of this at all. In cases like this, we can make use of the other null coalescing operator, which is the two question marks and the equal sign. What does that do and how does that work? Let's say for example, these are defined as null here, for whatever reason during our software, we're not really giving these any values, they remain null. Well, maybe one of them has a value, but for whatever reason some of them can still be null. We come to adding these to the list, we only want to add the values where they're not null because we can't add null things to a list. Even if we try, it's not going to letters. What I want to do is if these have a value like this, for example, then I want to add it to the list. This one has a value of 4567, so I want to add it. However, if they're null, then I want to add zero instead or some other default value. Basically, I don't want to add null because I can't. There is actually quick way of doing this. What I can do is use this null coalescing operator followed by a zero. Let's reset that. What that does, if this variable here is null, then it's going to assign zero into this variable, then add that to the list. If this is, if the left hand side of this operator evaluates to null, which it does because it's null, then this variable will receive the value of whatever is on the right side. Remember, this could be a simple value, It could be a method that has a return. It can basically be any expression that can be evaluated. So let's just put zero here. What we can do, we can do this for all of these. We want to add all our cost of the bills, for example. We want to, of course, add the cost of spending our money on useless things. Now look what happens if I run the program and add a break point here. Now I go down to my totals here and expand that. You can see the list has all the zeros here, which is the default value as you can see here. Not only that, you can see this reflected in the variables themselves, they now have the value of zero. To illustrate that point, I'm just going to change one to something like this. I'm going to run the software one more time. If I come to the locals window down here, you can see this variable has actually retained this value. It's been assigned into it, it now has a new value, 4567, and this is now reflected in the list as well. This null coalescing operator to question marks in equals. If the left side is null, then the left side will receive the value on the right hand side. That is how this operator works. Just like before. I'll write a code comments, so you can see this illustrated right here. If the nullable type evaluates to null, for example, cost of shopping is null and it's null at that point. Then evaluate whatever's on the right hand side of this operator and assign it to the nullable type. Obviously, if the nullable type is null, it receives the value. Those are two null coalescing operators in C Sharp, how they work and also why they're useful. It's nothing you cannot already do with a condition to check the value, but it is a nice short cut to minimize code and also development time. 73. 18-1. Named and Optional Parameters: I'm going to introduce a couple of tips now that you can do when calling methods in C Sharp. This is to do with passing the parameters in. I'm going to talk about what's called named parameters and also optional parameters in C sharp. Let's look at this example here. It doesn't really do much. I have a sample method, it takes in various parameters, all of different types. We have a video game object, a couple of numbers, a string and also a booling. Inside the method, we're just outputting the title property of this game object, which we specify up here in the constructor. Next we're adding the two numbers together and displaying the result. Finally, we have a condition. If the value of this booling variable is true, then we're outputting the message here. It's a bit of a gauntlet of tasks. It doesn't really have any purpose in the real world. It's just for the purpose of this example. When we call the method, you can see we're setting up a new object here. And then we're calling the method passing in that object and also the remainder of the parameters when I run the program. You can see it pretty much does exactly what it says so far when calling methods. We've been calling these methods with the parameters in order which they appear. The game object is First we pass in the game first, followed by number one. Number one. Number two, you can see all in order which they're specified by using something called named parameters. We don't need to specify the parameters in order. Let's take a look at an example of that right now. Say I want to switch the position of these two parameters here, Hello, and also the Boolean true. Now I want to specify the bolen first. What we do, we take the name of the parameter here and prefix it with a colon, just like that. We're going to specify that first, now we're going to specify the message. Afterwards, we do exactly the same thing. We take the parameter, we add the colon, and then its value. Now I've traded the ordering of these two parameters. In order to do that, I have to specify the name of the parameter just to tell the system which one belongs to which one. We just fix that with a colon here. When I run the application, now we have exactly the same result. These are named parameters. You can see we only changed the order of the last two parameters. The first three remain in the same order. That we don't need to give these a name because they're in the same order. However, if I want to name my first parameter and put it somewhere entirely different, then I'm going to have to name every single parameter. Otherwise, we're going to get an error here. In this case, I don't need to name the first three because they're in the exact same order from the start. But if I move this game all the way to the end, for example, and give that a name look something like this, then I'm going to get this error. And that's because I need to prefix everything else with the name. Now you can see the error has been resolved because game has been moved out of position. And that was the very first one. Therefore, there's no ordering at all. So they will all need a name. In this case, that's the power of named parameters. But why is it useful? Well, you could argue it improves readability. You could say from the actual call itself, assuming this method was locked away in a different class or a different file, you only have this visibility on your end, you can clearly see look number one has the value of this number two, as this it gives you a bit more information about the call. However, it does create a bit more code in your application. Another reason, perhaps a developer is working on this method. Here, the method isn't quite finished yet. They have maybe five parameters for example, but maybe soon they're going to add a couple more. Your job as a tester is to test the method. You're testing the method with these five parameters, but you don't know if the developer is going to add more of them later. So what you can do, you can use named parameters here to conduct any testing you wish to do. When the developer then adds two more in any order, it doesn't really matter, Then you know that your parameters aren't going to be passed into different ones by accident. For example, if the developer then adds two more integer parameters, then we know that number one and number two will be 5.3 in this case. If the developer adds 3.4 for example, we're not accidentally putting these numbers in those slots. In cases like that, it's quite useful when you're not accidentally passing parameters of the same type to different parameters. You're literally saying, okay, this parameter called this will receive this value. That is quite useful. It's not only methods. You can do this in constructors and a couple of other things as well. If I go to this video game class where we've specified this parameter to the constructor, you can see the constructor just takes one argument, which is title. Just like when calling methods, for example, I can prefix this with title and it's going to compile just fine. We're not limited to method calls with named parameters like these. We can also use them in constructors and other things like that. So let's talk about optional parameters now. What does that mean? If you have an optional parameter, then you can give the parameter a default value if no parameter is specified. For example, let's look at this display message Bolen. Right here, we're passing in the value of true. Let's just say we don't have to pass in a value. But we can, if we want to, what we can do here, we can say, okay, if this parameter isn't passed into this method display message, then let's just set it to a default value of true. If the parameter is omitted, it's not there. Then when this method then gets called, it's just going to initialize this to true. If this is true here, it's going to output the message. We can take a look at that right now to see if that works. You can see the messages being output. Similarly, if I change this default value to false, then we're not going to see this message at all. It won't say hello, which it doesn't. When specifying optional parameters in C Sharp, they have to go after the required parameters. For example, if I make message an optional parameter, I just initialize it to a default value of an empty string like this. You can see I have a little error here when I try and compile the application. For example, if I just set this to true, you can see there's an error. If we come down here, we can see this error here. Optional parameters must appear after all required parameters. All optional parameters must come at the end. Here you can have as many as you want. For example, we can make message a default value as an empty string and also display message as a default value of true. Then we can actually remove these values. We can even go as far as saying, okay, let's initialize these two numbers to zero if they're not specified. So you can see there, then we don't need these for example. But it really does depend on your purpose and what you're aiming to achieve if we run the application. Now we can see adding the two numbers together, a zero because we're initializing them to zero, because we're not specifying the parameters. Pretty much the only thing we're doing is outputting the title of the video game here when we actually call this method here. If we look at the parameter list now you can see there's a bit more extra information here. It requires a video game because this is a required parameter. However, you can see optional parameters now have these square braces around. It also gives you the default value 00, an empty string and also true. It does give you some feedback on what is required when trying to call this method as well. You can see how these optional parameters are represented when trying to call your methods. Again, you're not limited to method calls. With this, just like before, you can use these in constructors and again, some other things as well. Delegates indexes. If I set my parameter to the constructor as a default value, as an empty string, then I no longer need this value because it's optional. When we run the application, we're just going to get an empty string. You can see there, there's no game title because the default value is an empty string. This is the power of named parameters and also optional parameters In C sharp. It opens up things to a whole new realm of possibilities. I hope this tutorial helped you and happy coding. 74. 18-2. The out Keyword: I'm going to talk about the out keyword in C sharp and why it's useful. Consider this example right here. This method, what it does, it takes in four parameters. What I want to do is add these two together and then subtract these two together. You can see I'm doing that here. I'm getting the result of the addition in this variable and the result of the subtraction in this variable. But how do I return both of these? When we talked about returns in methods, we can return a type here, but we can only return one value. How would I maybe 235 different things out of a method? Is that possible? Well, in short answer, yes, we can use the out keyword in order to do this. And you see the out keyword used in many instances. For example, a method might do some operations and return a result. But we also want to return maybe whether the method was successful or maybe a log of any errors that happened along the way. We not only need the result out of the method, but maybe we need more information on how it handled things, you know, what errors occurred or pretty much anything like that. So let's take a look at the out keyword and how it's useful. Now the out keyword on how it behaves, it's very similar to the ref keyword. If you didn't watch my tutorial on the ref keyword or passing types by reference to methods, then I highly recommend you check that out. What I'm going to do here, I've defined two local variables here, result, add, and results subtract, and I've initialized them to zero. Right now I'm outputting them to the window. Inside the method, I'm doing pretty much the exact same thing, but I want these results right here to reflect in these variables so I can output them to the window, because right now I can't get these two values out of this method. How do I do that? Let's take a look at using the out keyword, what I can do inside the parameter list here. For this method, I can add an extra parameter with the out keyword. What I want to do, I want to return both of these values out of the method. I'm going to have two out variables here. The first one is going to be the result of the addition. The second one is going to be the result of the subtraction. Now, because these are getting passed into the method with their own types and own names, I can't then give them a brand new type. I remove those. That is pretty much how it works. Now you can see an error has popped up here. And when I hover over that saying there's no argument given that corresponds to the required parameter, basically I need to specify two extra parameters. The number of parameters matches the definition. Here, I need two more. When you have the out keyword in the method declaration here, you also need to specify the out keyword when calling the method. This is what I'm going to do here. If you watched my video on the ref keyword and passing value types and reference types to methods, you'll know that when we pass something to a method by reference, we can modify the values inside of the method and we're referencing the area of memory where these variables sit. This is what the out keyword does. But there is one subtle difference between the ref keyword and the out keyword here. That is, variables don't have to be initialized before passing a variable with the out keyword. What do I mean by that? Well, let's actually see if this example works First, before we get ahead of ourselves, I'm passing in 20 values as out keyword parameters. They're coming into the method, and then we're actually setting the values right here. Let's take a look. You can see we get the expected result. Two plus two is 4.6 minus four is two. It does work. And we're actually getting both results of these returned out of the method. But it's not really returning out of the method, it's just modifying these two valuables as they're being passed by reference into this method, then we're just outputting the results. I said before, there was one subtle difference between the out keyword and also the f keyword. And that is that when using the out keyword, variables being passed in do not have to be initialized, that means they don't need a value. It's still going to work when I run the software. Now you can see they have values. And that's because when things are passed into a method here, we need to give them a value. If we don't do that, we're passing in a variable. Here you can see there's an error and it says result ad must be assigned to before the method finishes. So we need to actually do something with these out parameters here. We need to do something with them, give them a value, initialize them, do something that is the subtle difference between out and ref. But generally, the out keyword allows you, in a way, to return more than one item from a method, and that's its main power. Really another thing, we don't have to define our variables here. We can actually define them all in one line. If I remove these variables completely between the out keyword and the variable I just type in, int, for example, for the data type. Now we're actually defining our variables in one line of code here. And you can see it looks a lot idea. So we're defining them here, then we're passing them in all in one. And then it's doing something, throwing them back out. And then we're outputting the results. So you can see we get the same results right here. So that's the power of the out keyword in C sharp. 75. 18-3. The in Keyword: I'm going to talk about the keyword in C Sharp. Now, I have a very simple example. Here I'm calling a method that adds two numbers together. When the method is called, we're stuffing the result of these in a variable, and outputting the result by adding two plus two, we get the output of four. How does the keyword come into this? Well, when we use the keyword in a method here, we can specify this before any parameter we wish to. For example, number one, what the keyword does, it prevents us from modifying this value at all. Then if we try and say set a value like that, for example, you can see the software won't even compile. When we highlight this and hover over it. It says cannot assign variable int because it's read only. It actually prevents us from doing anything with this variable. Here again, we could put this on any number of parameters we wish to. These are simple value types, simple integers. Let's take a look at how this works with objects. For example, you can see here I have an example with an object here, like video game for example, I'm setting the title of the game through the constructor to Minecraft and just outputting the game's title. But if I try to modify this object in any way when specifying the in keyword, then it's going to throw a similar read only error. You can see here I'm erasing the title by setting it to an empty string. But it's saying it can't be assigned to, it is read only. Similarly, if I try and create a new instance from this completely, then I have exactly the same error. This is the power of the keyword in C sharp. It prevents things like methods from accidentally modifying any of your parameters which you wish to pass in. If you know this method is not responsible for modifying your parameters in any way, then you might want to consider specifying them with the in keyword to protect your data and avoid methods from changing any of your data and having unexpected things happen, which can happen quite a lot, believe me. But the beauty of the keyword is yes, you could pass a constant or a read only variable in here, for example. But maybe your objects aren't read only or constant, but you just want to make them temporarily read only just for the duration of the method. That is the point of the Q word in C shop. 76. 18-4. The params Keyword: The Perms keyword in C sharp. It looks just like this and it's short for parameters. But what does it mean and what does it do? Let's take a look at this example. Right here I have a method that adds some simple integers together. It takes four parameters, it adds them all together, and outputs the result. The method takes them in from whatever's calling it. We're adding 224.5 Let's output the result. There it is there. For example, if I want to add two numbers together, maybe I want to add three numbers together. Or maybe 17 numbers together. But I want the same, I only want one method. I want the same method and one method to add all of these numbers together. How do I achieve that? Well, maybe I could create a custom object, for example, feed in all the numbers. Or maybe create a list and add all the numbers to the list. Then I can pass the list to this method. Essentially, that's what the prams keyword does. In this case, when I use the Prams keyword, I type in Prams here into the method signature. Here it is a parameter itself. Next I put the data type. The data type can be pretty much anything behind the scenes. It uses the object data type, which is what all data types derive from anyway. But we're using integer. We can use custom objects if we wish. Custom instances, it doesn't really matter. I'm just going to call this list because this list is going to contain all our numbers that we're passing to this method. Now when working with lists, we're going to use something like a loop to loop through every item in this list. So we can add all the numbers together. Let's do that now. We initialize a variable to zero. This will keep a tally of all the numbers that we're adding together. That should work right there. We're looping through every number in the list. We're keeping a running tally, adding everything to this result here, and then outputting it. We're going to get the same result Here, you can see 13. Now this is the power of the params keyword. Watch this. Okay, I've modified the calling argument here to add a lot more parameters to this list, but you can see it hasn't caused any problems. This is the power of the params keyword. If we were to build up a list, for example, and pass this into the method, then we would have to modify the list in this way too. But you can see how this doesn't cause any errors at all. We can compile the software and we can run the software, and we have our expected result right here. This is the power of the params keyword. It allows us to use one method to accept a varying number of parameters of the same type, and then it can work with that information. Now, there are a few rules associated with this. There can only be one params keyword per method declaration, for example. We can't have two of these like, so it's not going to work. Secondly, the params keyword must come at the end of everything here. If I have more than one parameter here, params must be at the very end. It can't be at the start, it can't be in the middle. So you can see an error has occurred here, because it must be at the end of the list. And lastly, the params here must be a single dimensional array. It can't be a two dimensional array, It can't be anything weird like that. So there's some of the rules associated with the params keyword. So that is the power of the params keyword in C sharp. Yes, there are other ways of achieving the same results, but the more tools you have in your toolbox, the better developer you will become. So that's the params keyword in C sharp. 77. 19-1. Enumerations - The enum Type: I want to talk about enumerations in C Sharp, otherwise known as enums. And the keyword looks something just like that. But what is an enum and why should I use it? Well, I have an example right here. Here I'm setting up four video game objects. They take in various parameters. Let's take a look at the class now. So you can see it takes a console, a video game title, a video game publisher, and a rating. So let's pay attention to this rating string right here. What I want to do, I only want to allow certain ratings for everyone. Ten plus teen, mature, 17 plus, et cetera, et cetera. I only want these values to be passed in and I only want to deal with these values. But when setting up these objects, you can see I'm putting them in here. But it's very easy to make a mistake. I could make a misspelling, maybe a lower case, something like that. If this application is connected to a database, then there's a bit of trouble. I'm going to be storing incorrect values and the whole system can get messed up. If someone wants to search for a game, for example, and the rating is wrong because it's been spelt wrong, then perhaps if they're searching by rating, this video game might never come up in the search. Lots of reasons why we need our data to be concise and accurate. One way we can tackle this problem of making sure that there's no spelling mistakes for this string variable. Rating, for example, is to use something called an enum or an enumeration. How do I set that up and how do I integrate it into my video game class here? Well, let's take a look. Let's come over to the right hand side here where we have our project. We're going to write Click, Go to Add, and then go to class. We're going to call this something that represents our rating. Now if we have a very large piece of software, we might want to be really descriptive with this. I think maybe video game rating is good. However, sometimes when you create an enumeration, you might have a class with exactly the same name, and you can't create a class with the same name. What a lot of people do when creating an enumeration is to add the word state or type afterwards. So every time they create one, it either ends in state or type. It's really up to you, it doesn't matter. But I'm going to call it something like this. So pay attention here, you notice it's a class here when I click Add, so if we come over to the left, now we have an internal class video game rating type. Well, we don't want a class, we want an enum. And there was no template for that, so now we have an enum. It's as simple as changing class to enum. We have an enumeration right here. So how does this work? Well, let's go to our video game class here and take our allowed ratings. I'm going to put them in here as a comment so I can reference to them. And I want to create an item in the enumeration for each of these ratings. So I want everyone ten plus teen, mature 17, et cetera. So I want all of these items in this enumeration. And the enumeration is like a list. So like a list of values. And this list isn't just a list, but it's like a read only list. We can't modify this information. It's pretty much read only, so we use it to refer to these values. It will all become clear momentarily. What I'm going to do is create some values for each of these ratings. In the enumeration I'm going to start with which stands for everyone. Once I've created one value, I put a comma and then a new line. Now I can do the next one. Now there's a problem. Once I've typed in ten, that's because in enumerations, your items cannot contain numbers or certain characters like this plus symbol. We're going to have to type this out. In this case we can say ten plus, and that works just fine. Let's continue. I've typed out a rough enumeration here you can see we have all of these values reflected in the enumeration. We can add more at a later date if we wish to. Now, how does this work? How can we put this into our class? Well, this is now like a data type really where we had a string rating before. We can use this enumeration right here. If we go to our class right here, we replace string with video game rating type. We also replace it in the parameter and also any methods we may have here. Also there. And it looks like we have one problem, and that's due to accessibility. By default, our class is internal, but because our video game class is public, we need to make the enumeration public as well. Now, all those errors have gone away. Now, we've actually changed the parameter to our constructor, to an enumeration type. Let's have a look how we construct these objects now. Now you can see there's errors on all of these right here. Let's try to change this teen one to use our enumeration. If I put a comma here, you can see the intellisens, the autocomplete has chosen our number for us. We're just going to double click that. Then we're going to put a dot. Now you can see there's a nice list here. If someone wants to construct these objects. Now they can't just put in any value. Look, it requires a video game rating type. You can see in the parameter list. But now we just can't put anything. We have to choose something from this list. If we don't, then the application won't even compile because there's an error. You can see how this enumeration forces us choose an item from this list. Now we can say teen, for example. Now if we replace each of these with the enumeration, you can see when we're constructing these objects, now it's going to look something like this. You can see this is a locked idea. But not only that, it forces people or pieces of software or anything else to not make mistakes in our information. You wouldn't really use this for something like maybe Blizzard or World of War Crafts because these are unique. However, perhaps the console could represent an enumeration because there's only a finite number of consoles. You know, you have the Playstation X box or PC. So this again could be represented by an enumeration, but for something like rating, this seems like a perfect candidate to have as an enumeration when working with enumerations. For example, maybe these video games are stored in a database. Now, this database will have the video game name, the title, and it might not have the enumeration full name in the database. It might have an integer like 01 or two. Each one of these integers might represent a different rating in the enumeration. For example, every one would be 010 plus would be one, teen would be two, et cetera. When you define enumerations in visual studio, there's an underlying type that means in the background. By default, each one of these has a value which is an integer. And I'll show you what I mean by that. This output one of these enumerations to the console window. I'm just going to output video game rating type teen. It's probably just going to say that on the window itself, it just says teen. But watch what happens if I convert this to an integer. So if I run the application, now you see it has the value of two. By default, there's an underlying integer in here. That's because by default the first item is 012345. This is done by default. It's default behavior, but you can actually change that if you wish. You can specify your own values for these. By default, it looks something like this. Everyone has the value of zero. This one has the value of 12345. This is what it looks like behind the scenes. These have these integer values. You can reference them with the number or you can reference them with the name. The choice is up to you. But typically, when you store something like this in maybe a database, or you're passing these values to a different piece of software, then perhaps you will be sending the integer just because it's smaller and it's easier to work with. This is why enumerations have an underlying type. Consider this as like an index for example. But like I said, you can configure your own types but also your own values. For example, I want this one to be ten, that one to be 2030, 40, 50. It doesn't really matter, the choice is totally up to you. And now if we output this again to the console window, you can see ten now has a value of 22, and that's because we gave it the value of 22. I don't know why we did that, but you can see that's how the principle works. So basically behind the scenes, it uses an integer, but you can change this to a different data type if you wish, like a byte or a long or something like that. The choice is really up to you, but by default. It looks something like this. If you want to change the type, you can add a colon afterwards and put the new type here. When you have a type here, then all of these values must follow the type you specify. Perhaps this might be something you don't use immediately, but it's always good to have this knowledge in your mind for when you want to apply it at a later date. But these are the possibilities and things you can do with enumerations. What is also quite common is if you have an enumeration, for example. All of these are video game ratings. You might not want to specify a rating, but the user, they're given a choice of six options. But what if it's optional? So what a lot of people tend to do, they'll define an item called non and usually give it a value of zero. Or they might give it a value of 999 and put it at the end, for example. But this is just an example of how you can make it optional. Non would be the optional field in this case. If it's not mandatory, otherwise you can select a rating right here. Again, that's just reflected by choosing the non item from the list. There's no rating for this game, in which case it's optional. Now, enumerations. There's a lot more to enumerations, and you can do a lot more with them. There's a static class called enum inside here, you can use various methods to do with your enumerations. You can get the underlying type like the integer we talked about before. And you can do various things. So we've kind of just scratched the surface here. But what I will mention is one thing to kind of keep your projects a little more organized. If we come over to the right here and right click our project, and what I tend to do is add a new folder right here, and I usually call this enums. Inside this folder, I put all of my enumerations just so they're tidier. So that way because they have the same file extension as a class, then you don't really get confused. You can hide away all your enumerations in an enum folder. If you remember when we talked about interfaces in the interface tutorial, how they have the interface keyword and not the class keyword, then you can create a folder for your interfaces as well. This is quite common. It just keeps things organized simply because they have the same file extension. If you have a very large application with hundreds of classes, you can easily find your enumerations just because they'll all be in a directory called enums, a nice bit of organization when working with interfaces And also enums, enumeration is very useful. It prevents any misspellings or anything like that. And it's very useful when you have a finite list of items, for example, consoles or ratings. Maybe when working with suits in a deck of cards or representing months of the year or something like that. But remember, enumeration items are read only like constants, so you can't assign anything to them, so consider them as read only when working with them. So that is enumerations in shop. 78. 19-2. Recursion and File Handling (File IO / System.IO): I'm going to talk about a brand new concept now. And that concept is called recursion. If you're familiar with computer science, or maybe you've done other programming languages, or even mathematics. Maybe you've heard of this word before, but maybe you haven't. So why am I on Google? I hear you ask. Well, when I started my programming ventures, recursion was something that really confused me. Have you ever seen the movie Inception, where the guy goes to sleep and then he's in a dream, but then he goes to sleep in the dream. And kind of plays with your mind and you kind of wondering, is he dreaming? Which layer of dreaming is he in or is he awake again? You know, it's very confusing. And the nested dreams in this movie always reminded me of the concept of recursion and you'll see why. But hopefully in this tutorial, I'm going to break it down into simple steps so you'll understand it a lot easier than I once did when I started learning. And I'll show you why. If you Google the term recursion, you get a description here. The process of defining a problem or a solution in terms of a simpler version of itself. For example, you can define an operation, find your way home as if you are at home. Do you see what I mean here? It's not very clear, is it? And the more you scroll, the more confused you get. It's just one of those things that you kind of pull your hair out over and when you look at the images, well, the images don't really help either. You just get this kind of picture over here of something inside something else and it's just repeating forever. So let me explain to you what recursion is. It helps by looking at recursion in C Sharp in Google, and it gives you a better explanation of what it is in terms of C Sharp. Recursion is a concept in which a method calls itself, and it is exactly that. In the world of C sharp, you define a method and the method then calls itself. Now, why would a method want to call itself? Well, if you have functionality inside a method to do something, then maybe you want to reuse that code. Why not? Programming is all about reusing code. It saves time, it's easier to maintain, and there's lots of other reasons to do that. This is what we're going to be looking at today, recursion in C sharp, and we're going to define a method that calls itself. We're over here in visual studio. Now what I want to do is set up a method that calls itself. If you watch any other tutorials on recursion, you'll probably see something where you have to work out the factorial of a number four. Factorial is one times two, times three times four. And then you set up a method to do that. I think that's quite a weak and boring example. I think we can use something maybe we can apply in the real world. I think a search feature is really good for that. What I want to do, I want to introduce you to my very bad music collection. Here you can see it's quite eclectic. We've got all different genres here. What I want to do is specify a search term and that could be any, it could be a band name, it could be the name of a song, anything like that. I want to return all of the music files that match this criteria. So we're going to ask the user for a search term, the user will type it in. The result will be the full file paths of all of our music files. Now this music collection is very unorganized, hence why we need a search feature here. I have a music folder here, and inside that I have a folder called even more music in there. I have all these new folders, and then I have music dotted everywhere. I think a search feature might be something good for this example. The problem, I need something to get the directories inside a file path that I provide the software. So if I provide the software, this file path here, I need it to get the directories. The second thing I need to do is to get the software to get all of the files in a directory, and check in turn each one of these files to see if they match the search criteria. It needs to do two jobs. And why is this scenario a good example of recursion? How can I apply a recursive method to this example? Well, I want to get the directories and the files for each directory in here. I want to do the same logic in here. I want to get these directories, these files. And then inside these directories, I want to check it. There's more directories then also get the files. The methods logic pretty much applies to any directory in here. I want to reuse the functionality. I want to use it here initially. Then I want to dig inside these folders. Keep digging until there's no more, and then check the files here. Recursion will be a very good example of something we can use for this particular scenario here. Let's have a look how we can do that. I'm over here in visual studio now. What I need to do is create a method. And the method is going to call itself. And the job of the method is to essentially search for a file that the user specifies. Let's set up that now. The first thing I want to do is ask the user for a search term. Let's do that. Then I want to accept the input from the user. Now I've got the search term from the user. I want to call a method. Let's set up a method that's actually going to do the searching. I'm going to call the method search. I think that's a pretty fitting name. Now, I need to define some parameters. What parameters should it take? Well, the first one, we need to know where the music is located on the system. We need a file path. I think that's a pretty good first parameter. The second one probably the search term. We need the method to know what we're actually searching for. The last one, perhaps a reference parameter and maybe that's a list or an array. This is going to collect all of our results. When you search for something, you might have one result, you might have no results. But you also might get ten results, like ten matches for your search. We can't just return a simple type, we need to return something like an array or a list. For example, I think using a collection such as a list here will be quite fitting. I'm going to call this results because it's going to contain all of our results that we find from our search. Now we have the path where the music is. We have the search term of what we're searching for. Now we have a collection here that's going to store our results. One thing you may wonder is, well, why don't we have this as the return value? Why do we need a parameter which is a reference type like here for example? Well, the truth is it doesn't really matter if I set this as the return type. I think it might complicate this example a little more. What I want to get across to you is how recursion works, where a method calls a method, otherwise known as a recursive method. If I set up a return type, then I have to return the value out of each call to the method within itself. I think it might complicate the example a little. I'm going to use a parameter for now, then when I've actually developed the solution, I'm just going to switch this to a return type so I can show you that example as well. That's the reasoning behind it here. It's just going to store the results. When developing recursive methods like this one here, it's always good to get the base functionality first. And that is what it's designed to do ignoring recursion completely. That's where the method calls itself. What I want to do is use the path that's given to us and use the search term and see if we can actually get some results from the root folder here. For now, we're going to ignore digging into folders and everything like that. What I want to do is get these files here, get all of the files for the given directory, And then in turn, I want to check each file to make sure it contains our search term. If it does, I want to add it to the result list that we've just created. Let's take a look how we can actually get these files for a directory and then check each title to make sure it contains our search term back in visual studio. Now if we want to work with files, directories, file path, or anything like that, there is actually a name space we can use. This is provided to us. We use the using keyword and then type in system and then O stands for input output. It's pretty much anything to do with files logging to text files reading from files, all things like that. It's a really useful namespace that we can use. It's not included by default. For example, before in a previous tutorial where we use the math static class and within math we can do various math functions. This is included by default because it's quite a popular library. When you create an application, you may wish to do a lot of things to do with math, for example, and many other things as well. However, not every piece of software you create is going to work with files. This is why we have to manually explicitly include this library. That's just a bit of information there. If you wish to use any other namespace for that matter, you can add them below within the system I namespace here. There's lots of things you can do. You can do all of this stuff here. Lots and lots and lots of things. But there are a few static classes you may wish to be made aware of. The first one, for example, is Directory, and this is a static class. Using this, we can create directories on our system just by giving it a path as a parameter. We can delete directories. We can get files within a directory that we provide. We can do lots of things to do with directories. This directory, static class, is really useful. Another one is a static class called file. With file, we can create files. For example, if we want to create a log file, we can delete files. We can check if files exist, we can move an open files. So lots of different things to do with files. The last one that's quite useful is the path static class. Path is really useful for working with paths. If we're giving our file path, we can get the file name from the path. We can maybe get the extension of a file. We can actually work with a full path and we can also join paths together. This is really good for working with directory paths. There are three static classes that you'll find really useful moving forward. And we're going to utilize a couple of these today when we develop our recursive function search. Here, I mentioned before that we want our method to get the files in the route directory just to start with, just to make sure it's actually working, what we want to do is get all the files in a given directory. We know this information because this is the path which is passed into our method. I want to get all the files within this directory here. To do this, we make use of the directory static class and there's a method called get files. Get files takes one parameter and that's the path where the files are located. Now the return from this method is a string array. Now this array will contain the full file paths for every file in this directory. If we come over to our music canal, it's going to get all of these files here. Each item in the array will contain the full file path. The full path on the system, that's going to be the return from this method, get files. I'm going to store that in a variable called files. That's going to be all the files in the given directory. Now what I want to do is loop through all of these files here and check that the file name, not necessarily the whole path. We just want to check the file name to check that the file name contains our search term. Here we need some loop here. I think for each loop might be sufficient. In this case, visual studio has kindly given us some autocomplete help here. I'll take it now. In this four loop, I want to check each file in turn and check that the file name of this file contains our search term. How do I do that? Well, when I want to check, I need a condition. I know I'm going to need an if statement here. Now, what condition do I need in the statement? Well, I need to get the file name from this path. I don't want the drive letter, I don't want the folder names, I only want the file name when working with path. As I mentioned before, a static class called Path is very good for this. There's a method called get file name without extension which will get the file name, say three. There's also one called get file name. You can choose which one you wish depending on whether you want users to search for file extensions as well. I'm just going to use this one. It takes one parameter and that's the path from this, this highlighted code here. This is going to get the name of the file without the extension coming over to our music. It's going to get this highlighted section right here, which is great. That's what we want to check back in visual studio. Now I know that that is the file name without the extension and without the path. I want to try and see if any of that contains our search term. In a previous tutorial, I covered working with strings where we did various things with strings, substrings, and things like that. Because this is a string here, path get file name without the extension returns a string. Therefore, this will represent a string. When I put art after here we have all these different things we can do with strings. There's a method here called contains. Contains. Takes one parameter, which is either a character, a string, or actually numerous parameters. A character and a comparison type. But we just want to use this string overload here. We want to check to see if it contains our search term. I think that is a pretty good condition. Now, there is a bit of a gotcha in here, which I'll reveal a little later, but for now I'm going to leave it. Now, we're checking to see if each in turn file contains our search term. That's pretty good. Now if it does actually contain our search term, then we want to add this path here, which is file, to our results list. Let's do that now. We use the add method to do that. We add the file there. If you don't know anything about lists, then I have done a tutorial on that. I recommend you check that out. Now it looks like we're doing something pretty good. We're looking at all the files in the given directory. If it contains the search term, we're adding it to the result list here, Because this is a reference type, it's going to remember what we've added to it when this method has finished executing. That is because it's stored on the heap, it is a reference type. Now what I want to do is actually call this method. Provide parameters to it. Let's do that. Now. The first parameter I need is the path where the music is located. Let's get that. Now, put that back in here. This is the route directory where all the music is located. The next parameter we've set up is the search term, which we take from the user's input. The last one we need to provide a list where we're actually going to store our resorts. I'm going to define a local one here to Maine. Set up a new list here. I haven't given it any capacity because we don't know how many resorts there are going to be. Just created an MT list here. I'm going to pass this into the method. When the method has finished executing, we have access to these results down here. That is because as I mentioned, it's a reference type. Now what we want to do is just display the results to the user. We could maybe use a four each for this as well. What I want to do, every time we have a result in results, I'm going to say let's just output the result. Then I could add like an if statement saying if there's no results, maybe I'll print the fact there's no results. Okay, so it looks something like this. Now I appreciate there's more elegant ways of doing pretty much everything in software development, but I try to write this in a way that you'll understand it's more easy to take in because this is just how brains work. Perhaps at the end, we can tidy it up that is optional, But what I want to get across is the principle of recursive methods. We have some base functionality here when developing software, we can test, just to make sure it works, we don't have to completely finish developing the software. I think now might be a good time to test this, just to make sure it works. Let's run the application now. Now, please enter a search term. Let's try searching for Aba, for example. Why not I go in my application, I type Abba says there's no results for my search. Why is this? Let's try and figure this out. I go back into the software now, I'm not getting any results out of here, but clearly I'm adding a result here. What is going on here? Let's see if we can figure this out. Let's put a break point here and run the software. Type in Ab. What do we have here? It looks like we're getting all of our files here. Are we actually reaching this break point where we're adding the value? It looks like we're not. So there's something wrong here. We can't seem to get the file name properly or something quite different is happening here. It looks like I've accidentally put path here when we should have file. At the moment, we're only searching the file path where the music is located and not actually the file name which is inside the loop. If that resolves the problem, okay, it looks like it's working. Now as you can see, nobody is perfect. Mistakes happen, but if you watch my tutorials on debugging and everything like that, you'll know how to fix problems yourself too. So it looks like it's working. Let's try something else real quick. I did allude to a gotcha earlier, and that is if I search for Aber, where it's lower case I hit, and it says there's no results. But clearly we have a song called Abba. What you can see here is there's a case sensitive issue. That's because Aber in the NP three is upper case, but we're using a lower case search term. So how do we get around this? Well, file is a string and the search term is a string. When we use strings, we have lots of things made available to us. What we can utilize is this method here called to lower. What that does, it converts all of this to lower case. Similarly, we can do this on the search term. Now we're comparing all of our search term, all in lower case, to the name of the file, all in lower case. Now, we shouldn't have case sensitive issues. If I run the application now and search for Aber, you can see now I have the result. Now we're ignoring case. That's pretty good. I'm going to do one more search and just search for maybe the letter E just to make sure we get multiple results. Coming back, it looks pretty good. It looks like we're getting all the file names that contain the letter. That's pretty good. Now, I think we're ready for recursion. We have the base functionality working. We're happy it's working for the base directory. Now we can introduce recursion. The problem is when you introduce recursion from the start, especially if you're not proficient, then if you have an error, it could be with just your core functionality. It's really good to get this working before you introduce the recursion to this. It makes things a lot easier. Let's introduce some recursion into this method. Now, I appreciate you may not get this the first time, but don't worry, you will get it eventually. There's a few ways we can tackle this problem. What I want to do, I have this search method that gets the files, which is pretty good. But also, I want to give this method the next directory in the current directory. Here, for example, we have our music directory. We're already checking the files, but I also want to get all of the directories here as well. Then inside each directory, I want to do the core functionality, which is to get the files, but I still want to get the directories too. Then inside here, I want to do the same thing, get the files. Are there any directories in here? Clearly, I need some function to get all of the directories in the current directory. Let's do that. Now, I'm going to put that up here. There is a useful thing we can do to get directories, and that's using the directory static class. There's a method called get directories and it takes a path. What path does? It takes our root path. And just like before, it returns a string array and each item in this array will be the full path of the directories in this path here. So I'm going to call that DR's for directories. And because we know that we want to go inside each directory, we need to loop through this as well without even thinking about anything. We know we need directories and we know we need to check each one without even worrying about the problem of recursion or inception or whatever you want to say. We know we need this functionality now. Once we have this functionality in place, we have to work out how to actually deal with this problem. What do we put in here? Do we need anything here? Do we need anything here? Et cetera. But now we have a bit of a template. Let's have a look at how to approach this problem. I'm giving the root directory to the method. What I might do in this situation is get all of the directories. And with the first directory I go inside it, then I call the method again, What it's going to do is exactly the same thing. It's going to get all of the directories and go in the first one. It's going to get all of the directories go in the first one. And now we're in the final folder. There's no more directories, so we can't go in the first one. So the last thing we need to do is get the files. So what we're doing here, we're getting the directories always going in the first one, always going in the first one. Until we've reached the very end, we get the files, we go out one, go in the next one, get all of the directories go in the first one, get all the directories, go in the first, et cetera. So that's what we're doing here. We're diving to the very bottom, which is the first thing we're doing. We're going inside, inside, inside, until the biggest dead end which is here. And then we're checking for files. So that's what we're going to replicate in our method. Now the first run of this right here, the search method, we're passing it the path which is the root directory for our music right here. What I want to do is get all of the directories like I just mentioned in the root folder. That is all of those here. That's what this four loop is doing. The first iteration of the four loop will be this directory here. Now we want to actually go inside this directory. What we can do, we can pass this method to itself. We can call the method from itself. Even what I want to do is call the method. Let's simplify this. Results will never change. We're not defining any new results, we're simply just appending to results when we have a result, When we have a match. We're actually initializing and defining results up here every time we pass results around. We just want to simply pass it around. When we call this method inside itself, we just want to pass this value inside. The only reason that we want to do that is just to add to it. We don't really need to do anything special with this here. The same applies with the search term. We're not changing the search term in here, we're pretty much asking the user for a search term. As far as we're concerned, it's pretty much read only inside this method. Again, we're just passing this through as well. Just like results, the only thing that really differs here is the path within our first directory. We actually want the directory that we're going inside. It's going to look something like this. If I just remove that a little, this is what it's going to look like. I don't know if you can wrap your head around this, but the first time this is run, we're getting the directories. We're looping through those directories. So the first directory, we're calling this method again. Now this method is being called with the first directory in the original path. Once it's inside that directory, again, we're getting the directories again until we reach the very end, which is here. Imagine this is the path being passed in Now, now there's no directories. This is going to have a count of zero. This for each loop isn't even going to run because if there's no directories in this result, this will be skipped entirely. Now when this is skipped, this method will not call itself because this is the only time the method calls itself. What it's then going to do is get all of the files. It's then getting these files here and checking to see if we have a match and then the method ends. When the method ends, we go back to the previous call, which is inside this loop. Then it's going to call itself again on the next directory, on the next iteration of the loop. Then it finishes, goes into the next directory. Here it checks for directories and files. Does this work? Let's take a look, why not enter a search term? So what I'm going to do, I'm going to give a search term for a file like this one. For example, hello, hello. Now, hello, hello is located in this folder, inside this folder, and hello, hello is not in the base directory. By searching for hello, I know for a fact that it's checking quite a lot of folders in order to find this file, that's a suitable test I could use. Let's run the program. Please enter your search term. Let's type hello in here. It looks like it's found it. You see this result, searching for subdirectories, it's gone inside two directories and it's finally found the file. Here, it looks like it's actually working. This is an example here of a recursive method, that's just a method that calls itself. We're just stuffing results into a parameter which is a reference type, it's a list. Let's do one more test just to make sure it's working. I'm going to take that Hello file, which is in here, and paste it in a few more places. I'm going to put it here. I'm going to put it here. I'm going to put it in here. Now we should get a lot more results. Let's run the program, type in hello. And now you can see I've found all of those instances of that hello P three, so it looks like it's working. So that's pretty good news. Now the thing when writing recursive methods, you need a way to escape out of the recursion. The recursion will not stop unless you introduce something like a condition, perhaps an if statement. Or maybe in our case, we have a loop that loops through directories and files. We don't have infinite directories, we don't have infinite files. So eventually this recursive method will stop. However, it's quite easy to have a method call itself endlessly, like in this example. If I have this method call itself with the same parameters, there's no way for this to exit. This is the danger of using recursion. When writing recursive methods, always check to make sure you have a condition or some escape clause. Otherwise your application will crash freeze, and you'll have a lot of unexpected behavior you see if I run the program, now I type in any search term, you can see we have a stack overflow. It tried to call itself 24,000 times before it eventually crashed because the stack is full of the stack area of memory. Always be cautious of this when writing recursive methods. So at the start of the tutorial, I said, oh, we could easily have this collection here as a return. We don't need it as a parameter. Now I've explained recursion, this can modify this code and have this as a return. Instead, I set up the return value here. I define this up here. Let's remove that part. Let's store the results in a results list here, because this will be our return here. I no longer need to pass this parameter in, and I no longer need this as a parameter, but I need to define a result in here. Let's do that now. Okay, What I've done here, I've added a return here to search, which is a list of a string. I've defined the result list of string inside the method here. Now there's a couple of things to note. The first thing I need to do is actually return this out of the method. I'm going to do that. Now the next thing I need to do, every time I recursively call this same method here. I need to store the return every time I call it recursively as well. Otherwise, we're going to lose this information. If we're down in the very depth of our folder structure, we've found some files, for example, like here. Well, we need to pass these out of the inner call of the method, because for example, I'm not storing a return here. What I need to do every time I recursively call this, I need to store the results here. Now you think, okay, it looks like it's working. I've defined the list, every time I recursively call itself, I'm remembering these values and setting it here. Then every time we have a match, I'm adding it to the list, and I'm eventually returning it out and printing the results. Let's take a look and see what happens. Let's say hello. It looks like we have a bit of a problem. This is where debugging is very useful, but I can tell you what is going on here. The problem is we've found some files in the inner depths of our recursive calls, for example, these files here. Now this is two folders deep, you can see here. Now what is happening is these aren't being remembered, because when this eventually comes out, we're resetting this value every single time we call this recursive method. And that's a bit of a problem. We're adding the stuff here, but we're also resetting it. Nothing is being remembered essentially, but we are actually adding information in here. If I put a break point type Hello, there are actually files here, but the problem is, it's actually getting reset. If I look at my Locals tab down here, I can monitor the results right here. I set a break point on return, hit a five. Now you can see I have one result if I come out of here. Now you can see results as reset to zero. As soon as I come out of here, nothing is being remembered. What is going on here. The problem is, well, it's quite a simple problem, but it's very hard to perhaps understand when talking recursively, What we need to actually do is add the results of this search to this list. We can't just replace the list with the results of the search, otherwise, we're forgetting everything we've learned so far. What we need to do is add everything from the results of the recursive search. And there's a method called add range. And what that does, it adds one or more items to our list. And this is the advantage of using a list over something like a simple array. We have these methods available to us. So let's take a look at this now and see if this works any better. So I run the application, I type in hello, and now we have all of our results. They're no longer getting raised through our recursive method. Calling this is why having a return, it adds a little more complexity into things. And that's why I introduced the example with a parameter first. Because this isn't getting reset every single time when we have a return, yes, we are defining the return here and initializing it to a new area of memory. But we need to remember to add our results from each recursive call, every time we call our method recursively. Now, I appreciate this is so much to take in, it's super complicated. But I, I broke it down in simple terms for you. If you watch this tutorial maybe two or three times. And maybe provide your own examples as well. You'll eventually figure it out and one day it will just click. I promise you this is recursion in C Sharp. Not only C Sharp. Recursion is in many programming languages and even mathematics and things like that. I hope you enjoyed this tutorial and thank you for watching. 79. 20-1. Final Project (Top Trumps Simulator Game): So the final project. What is the final project? Well, let's take a look. The final project is optional, but I highly recommend you apply all of the knowledge that you've learned so far and give it a solid attempt. Then you'll officially earn the title, the unofficial title of C Sharp Computer Programmer, or C Sharp Software Engineer. Sounds pretty good, doesn't it? So for the final project, we're going to be simulating a top trumps game. Now if you're not familiar with top trumps, it's basically a deck of cards. And the deck of cards is themed for whatever you want, really whatever you want to buy. For example, you can have a dragons with mystical creatures where you have wizards and kings and dragons and things like that. Each card has a character, this one's called Dragon for example. And he has various stats like strength skill, magic power on fear factor. However, if you buy a deck with superheroes, they might have something totally different with different character names. But generally each deck of cards is themed. When you create your version of this in C sharp, you can choose whatever theme you want. The Sky is the limit, Just use your imagination how the game works. Well, I've included a complete specification that explains how the game works, but also some assumptions you can take when developing this solution. I'm going to show you a demo now, roughly on how it works. So here is the specification right here, don't worry, I've included this in text format, so do refer to it a few times when sort of planning out your project and how you're going to tackle the scenario. I give a brief description of what it is. I've provided some links so you can do some further research. Now, this is a two player game. We're going to be assuming there's only two players playing. And I've put a list of assumptions that you can make when creating this project just to make it a lot easier. I don't really want you to spend weeks and weeks on this. You can if you wish to, it's no problem at all. But I think using this specification, you know, a couple hours a day for a week or so, I think that's a good amount of time to sort of train your recent knowledge and develop a nice piece of software to show your friends, family, or whoever you want to refer to the specification on how to get going with that. I'm going to show you my solution now on how I tackled the problem so you can get an idea of how it works. So when the software is first executed, we're just assuming player one goes first. Player one can press Enter to begin their turn. Now it's player one's turn. The player one has five cards and player two has five cards. So they have five cards each. So that the cards represent a character like a dragon or a king, for example, something like that. Here I have totally random characters. That's, you know, how good my imagination is. A randomly selected card or character from my hand is played, and that is the teddy bear. Now, the teddy bear has a height, a weight, magic power, and a fear factor. Because it's a teddy, it's quite small, it's not very heavy, It has no magic ability and no fear factor. So it's actually a very bad card. Now the idea is I want to pick the highest stat here, and I hope that my opponent has a stat which is less than mine. So if I pick height, say 1 meter 45. So I just choose the number one here. I press Enter. Then the player, the other player defends with Harry Houdini, who's a magician. But he has a height of 5.7 So the teddy bear is not taller than Harry Houdini. So the teddy bear loses because the teddy bear's height is only 145. But Harry Houdini is 57. Player two wins. But because player to one, player two takes the teddy bear card, player two retains their Harry Houdini card. And now it's player two turn to go. So if I hit Anton, Now you can see player two now has six cards because they won the teddy bear. Now it's player two's turn. The randomly selected character is Picchu. Now Picchu has quite good magic power, but quite short. And it's very light as well. And there's not much fear factor. So I want to play magic power because it's quite high and I hope that I can beat the now player one's defending card. So let's take a look look at this. The other player defends with Darth Veda. But I chose magic power, which was 75. However, Darth Veda only has a magic power of two. So I won. I won again. Now because I won again, it's still my turn. So it's still player two's turn. Now you can see I have seven cards. The winner of the game is the person who has all ten cards in this example, because there's only ten cards. If you create 20 cards, then obviously the winner is with all 20 cards. Now, there's a lot of assumptions here. You can see I'm randomly selecting characters from the deck which the player each player has. Whereas when you actually play this game in person, you take the one on top of the deck. So, I'm using a lot of assumptions just to shorten the sort of lifespan of this project. You know, I don't, I don't really want you working on this for 34 months and pulling your hair out. I don't think that will be a very fun first and final project for you. So there are a lot of assumptions, you know, it's not really mandatory. Add your own twist. Add your own flavor. It's really up to you, obviously, I've just played Picature, and Piccature has been selected again. So you know, it's not a perfect application, so don't worry about it being perfect. It's just to train your knowledge and things like that. So it's just a bit of fun and I think you'll have quite a good time with this here. We've got the mini devil, We're fear factor four. We're doing pretty well. We have nine cards now we have Harry Houdini magic power. And it looks like we've won the game. Player two got all ten cards totally destroyed, player one. Do we want to play again? Yes or no? If I press no, then thank you for playing. Press Enter to exit. That is the final project. Again, it's not the solution, It's just a solution. You can do whatever you want with whatever characters you wish, but try to apply a lot of the things we've actually covered in the course. So here I've created, on the right hand side here, I've created four custom classes. Here, I've put them in a separate project. And when I open the main method right here in the program class, you can see there's not really much code in here. That's because we've separated it off into, you know, logical containers. I have a game controller class that manages everything to do with the game, the turns, and everything like that. I have a player class now, the players, it models the players. And a player holds a number of characters or cards. And the character or card class is responsible for all the characters in the game. So you can see how we're using the knowledge we've applied. Where we take a class and that class is responsible for everything to do with what it's called. So the character class deals with characters, the game controller deals with how the game works, et cetera. So that's really how it works. We're taking all the knowledge we've taken and we're applying it now. So that is basically my solution towards the final project. You know, Planet Planet. Use some notepads. Use some paper. Use a pen. Have a good think about how you're going to tackle the problem, how you're going to organize the problem, and what techniques you're going to use, what loops, conditions, and things like that. I hope you have fun with this. The final project tests your knowledge on many concepts of the things we've covered so far. So classes, objects, instantiation, if statements, switch statements, conditions Boolean and logical operators. Four loops, wire loops, lots of different loops, methods and much more. So it's a great way to take all of that knowledge and apply it to one piece of software. How long will the final project take? Well, if you enjoy programming and you want to be a programmer, then this should not be a concern at all, because practice is always a good thing. If you're a total beginner when you started this course, then perhaps spend a couple of hours each day for a week or so, something like that. Like any other language, French, German, Spanish. You're not going to absorb all the information in one run through. It's just not realistic. But use the course materials as a reference point for the final project. If you're developing your final project and you can't remember how to do a wire loop, for example, then just rewatch the wire loop tutorial again just to get a refresher. Even professional computer programmers use Google and various other websites as a reference point, and sometimes they do this. Daily programming is all about thinking outside of the box and applying lateral and logical thinking. It is not about remembering syntax and regurgitating syntax, so don't be deterred by this at all. So I've included my solution for the final project, but I highly recommend you just do not use this. Do not look at it until you've finished yours. Then you can use it as a reference point to perhaps, maybe improve yours. Or look at the differences between my solution and your solution. Remember, there's not one solution to a problem. There can be multiple solutions and all of them being correct. But use it just as a reference point when you've completed your final project. Send it to your friends. Send it to your family. Upload it to Youtube for example. And send me the link. I would love to see your final projects and how you interpreted this specification and put your own twist on it. The last thing I want to say is, good luck with the final project and good luck for your future programming endeavors. Finally, thank you. Thank you very much for watching Take care. 80. 20-2. Course Summary (Where do I go from here?): Now, all good things must come to an end. But if you've made it this far, then thank you for watching. If you have any queries, problems, niggles, questions regarding any of the content in the entire course, then please leave a message on the content itself or send me a message. I'll be more than happy to help also review the accompanying project files if you haven't already. Most lessons in this course have accompanying project files and feel free to expand on them, learn from them, but also add your own twist to them. The limit is your imagination. The big question many people typically have after finishing a course is, where do I go from here? Well, I'm not going to leave you hanging. A lot of people do, but I'm going to give you some ideas. It does depend what your goals are. What are your goals? These are unique to you, They're personal to you. For example, maybe you're looking for employment. You want to get employed by somebody. Or maybe it's a hobby. Maybe you want to create a phone application to make money. Or maybe you want to make video games in Unity or just to try a new challenge. Something totally new. So it does depend. But the secret and common ground with all of these is practice, practice, practice. C sharp is not too dissimilar from a real spoken language like French or German or Portuguese for example. The more you use it, the better you will become. It's only natural. And similarly, the less you use it, the more you will forget. So in your free time, I recommend creating small software applications to solve your everyday problems and make your life easier. Not only that, it's quite fun as well. I've made lots of different pieces of software just to make my life easier. For example, I've made a music renamer when I have itunes, for example. Sometimes it doesn't take the file name, it takes a hidden tag inside the MP three, for example. So I made a piece of software to inject that tag into the MP three so that my itunes looks really nice and it's all automated. I don't have to, you know, rename every single song to give it the correct artist or title. For example, this is very easy to do with a lot of the tools and techniques we've covered in this course. Things like when free items come up on Craigslist or things like that, I can play a music sound. So anytime somebody is giving something away for free, my laptop starts playing music. And then I know something new is in the free section and I can instantly contact the buyer and, you know, arrange collection of that. You know, the limit is your imagination. And lastly, I've created a Youtube bulk uploader. What happens is, if you have maybe ten or 50 videos, you want to upload to Youtube, but you don't want to type out all the titles and descriptions and things like that. So I've made an application where I can take 50 videos, for example, drag and drop them onto the software. And it populates the video title and description and even the tags from the name of the video file. And this saves so many hours. And this is actually a commercial piece of software now. So not only does it practice my programming skills, but it also earns money on the side. So there's a lot of ideas there you can, you know, take on board and apply for your own specific scenarios. Another thing you can do, which is really, really good, is take online coding tests, like little coding challenges. So for example, there's two websites you can use. One is called Hacker Rank and another one is called Lite Code. I'll show you those now. Now each one of them has lots of different coding challenges, just like I presented the final project with the top trump simulator. But typically, they're a lot easier. For example, draw a pyramid, which we've covered in this course, or draw a square or find the queen, things like that. So quick challenges that test your lateral thinking, which is thinking outside of the box. So not only do they test your knowledge of C Sharp and perhaps your memory of the syntax, but more importantly, your application of a Sharp When you're presented with a problem, it tests how your brain works, how you understand the problem and find a solution. Usually these challenges are very unique and very specific. You can't really Google them and find a solution, for example. So if you practice these coding challenges a lot and home your ability on solving them, improving your lateral thinking, then this will make you very attractive to potential employers. Employers do not look for people who can regurgitate and remember syntax. They look for people and they encourage lateral thinking. And these online coding tests are perfect for that. Not only that, these two websites that I've suggested, they track which exercises you've already solved. And they create a profile like a little leader board. You know which ones you've solved. And I don't see any problem in printing this off or sending it to a potential employer. Then they can actually see what challenges you've done. And they can see that, you know, it's not just a career you might want or a job you actually enjoy doing this. And this is what they look for and this is what separates you from other people. And again, it's not only all about getting a job. Even hobbyist people love these coding challenges. You know, it really works your brain. It's a really good training exercise for your mind, so I highly recommend online coding tests. One more thing you can do is practice sample job interview questions, even if you're not planning on becoming employed. Because they really test your knowledge and put you on the spot when you remove this course from your laptop, for example, say you cover it with your hand or a book and actually ask yourself, what is polymorphism? Can you answer that question without looking at this course or googling it for example? Is that possible? What if I asked you, what is method overloading or what do I mean when I say abstract or abstract class? And what is encapsulation and how does that differ from, you know, another term? Can you honestly answer these questions? So this is how you really test yourself, whether you understand the principles. It's easy to watch someone else talk about something and say, oh, okay, yeah, I understand it. But if you cover the material with your hand and hide it from your view, can you honestly say, okay, polymorphism is this. So it's one thing, reading something and understanding it, but it's another thing, reciting it back in your own words. And that is very important not just for getting a job, but also really understanding everything covered in this course. So I do highly recommend doing this as well. So the last thing I'm going to mention in terms of what shall I do next, why you took this course. Some people may have taken this course to move onto something else. Perhaps you wanted to do game development in Unity. Maybe you wanted to develop websites, so you needed to know the sharp. Then you may learn the Spot Net, for example. Or maybe you want to create forms for a desktop application or a mobile application. You can apply sharp to all of these scenarios, but they require more knowledge in order to successfully fulfill the role or fulfill what you want to do. But in terms of knowing and understanding and practice in C sharp, this course will be very useful for those applications. I can tell you that 100% if you want to start creating games in Unity, you will find that you'll know pretty much all the C sharp. You need to know, or at least know how to look and research for any new methods and classes you wish to use. Any required knowledge to create video games in Unity will evolve around understanding and learning the Unity engine, for example, which is very different. But in terms of C Sharp, you're covered again for creating mobile applications. The C sharp already covered, Perhaps you just need to learn a few graphical or niche things to do with mobile applications. So again, this se shop course will be a perfect foothold for whatever you want to achieve. Whatever your end goal might be. So the last thing I'm going to say is, again, thank you very much for watching. Do not forget to share your final projects with me if you wish to undertake those. If you have any questions, send me a message and leave a comment. And just let me know how the course was for you. And perhaps in five to ten years time when you're a professional software developer, maybe you can send me a message and just let me know how you're getting on and tell me whether this course helped you in the long run. I will be creating more courses, so feel free to check those out for the final time. Thank you very much for watching Take care.