Solidity Tutorial for Beginners - Full Course

1. Welcome to Solidity: Your Journey Begins Here!: Welcome to the ultimate Solidity Smart contra course for complete beginners. In this course, I will guide you step by step to take you from zero to kick start your career as a solidity developer. So, that's diving. We will started with the fundamentals of solidity, like variables, functions, and arrays, and then we are going to build a small project like a calculator so you can practice what we did. Next, we are diving into intermediate topics like mapping, strap, loops, and modifiers and then use all those in a letter complex project class booth. Class Smart contrast and deploy all those in SupoyaTsNt. Then we are going to the advanced topics like require statement and events. So you will learn how decentralized applications like Opens talk to the blockchain and get the updates and the real time words using solidity events. We will also explore the inheritance and how to contract can talk together using something called interface. At the end of forces, I will give you an exercise challenge so you can apply all everything you have learned in this course. Okay, it is dived into the world of blocking development, CEO and the first lessons Sala 2. What is Solidity? Unlock Its Power to Build DApps: T. Solidity is a programming language that creates mad controverst and instructs them how to behave. That's it. And the life cycle of SMAT contract, first, we create a code using solidity, a normal code and compile it to the P code 01 and then run it on EVM Etherium Virtual machine. Okay? It's basically a server that creates your code that run your code. So, what can you build using solidity? Actually, Amazing things. First, dabs. So what is deps. To better understand dabs, I give you an overview what is a traditional applications. In traditional applications rely on a single, a single entity or organization for their functionality and data storage. And that's create what's called centralization arrays, which means if the server goes down, so the data is lost and the application will fail. Or if an attacker hack the server, so he gets the fell access to the network and stall the data. So that's why we transfer it to the tabs, decentralized applications. So decentralized applications store the data in multiple nodes into the blockchain around the world, which means your data is safe, and if some notes goes down, the data will be safe because multiple Nuts has the same data. And an attacker cannot get the full access to the network unless successfully hug every nuts in the network, and that's nearly impossible. Another thing is decentralized social media. Basically, it is a social media like Facebook, but decentralize. Another thing is DoS, decentralized autonomation organizations. In Taos basically is an applications managed by SMAT contract, not central authority, which means the people, the members, create the proposal. For example, say, Hey, please add this feature into the app. And this proposal get voting by the holders and then if the proposal goes through, so the holders create a SMAT contract and add it to the applications. Opposite to the traditional applications when the CEO or the organization decide everything and control all the decision of the applications. Another measle things. That's the biggest one NFT, non fungible tokens. NFTs is a digital asset. Create ownership of specific items. That's it. And the biggest case of the NTs is digital arts also in games. So in games, the NFT or the blockchain gives the players the possibility to trade or sell their items. Of course, you can create your Crypto, like theror bets coin, dash coin, et coin. And the good thing here, if you have, for example, a platform or decks, so you can create your own crypto to your own platform. That's mazing. Actually, in the coming lessons, we are going to create our own stable coin. Okay, the salary. Blocking developer gets around 110 k 250 k a year. And the solidity developer get one get 120 K to 200 k. So let's dive into the difference between Web two and web three. Okay. Web three. So before we three, user use the app, the applications like face and the application store the data into a server and somewhere in the cloud, so in the database. But a single server, which means another server doesn't has the same data. But in web free, user use crypt wallet, which the wallet hold their private key. And the wallet use DAPs, decentralized applications. Then the application that store the data in multiple server into the block chain around the world, which means your data is stored in multiple server around the world, and you are the own who control this data. So let's create our first SMAT contact. 3. Hands-On: Building Your First Solidity Smart Contract: So we are going to Remix, the online ID for creating Smart contact. Okay, RmxRmx Here it is. Okay, here is the remix online ID. He gave us a beautiful interface to interact with the SMAT contract. This the functionality, and even deploy it into the block shehet Okay, there's a folder here. I was created. So it is solidity tutorial. Ok are going to create another file, call it, for example, file. This icon for directory. These four files, okay? Let's say hello. Okay, dot SOT. Dot SOT is to tell the ID, this is solidity file. Okay. We start with a command called PDX, Speed x, License. Unify upper. Okay? T. Basically, this is to specific the license, okay? Let's say IT, which means open source, so anyone can clone it and use it. You can use another type like license or something, then the keyword contract on dact is hello. Hello contract, okay? Okay. Strength. Strength. Let's say head equal? Okay, high solidity. Kids in hair, does it? Yeah, he say Sears fine doesn't specify require compiler version. Consider add pragma solidity. Yeah. This told me you have to specific to specify the required version compiler. So in the solidity file, you have to tell the ID which version of solidity want to compile your contract. Okay? To do this, we write Pagn Solnit t say. So it Okay, Tata. So after this, we specify, so the ID. Hey, our contract, please comply with zero dot at 26 version of solidity. And this and this one, it this version, 0820 says above. This one above. So for example, zero dot eight dot 29, for example, yeah, we can compare it to it. And this icon have to compile solidity compiler. Okay, I market auto, so let's disable this feature. We can compile it, compile successfully. Okay, look at here. This is the version we specify to compile our contact, Okay? And plus here, this and above. And this icon have to deploy and run transactions. So for deploying our contract. Okay, here's the virtual machine RMx. Okay, for testing, a block chain to test to deploy your data, just for testing. Here is an account with a fake ether to taste as well. And yeah, here we choose which contract we want to deploy. It's a hello because, of course, we are just one. And click the bottom, deploy the transaction go through. And here in the bottom, we have our contract. Let's say we have to market this public. Obanoc and the point. No, you have to compare it and delete this one and this one. Okay, here is our variable. Hello. Inside high solidity. So, congratulations. You create your first SMAT contract. Okay. Don't worry. If you don't understand what is this string, public? Hello. What's going on here? Don't worry. We go step by step until you create your bests, not just a simple contract like this. Okay, let's back to the presentation. 4. Solidity Basics: Variables, Functions, and Arrays Explained: So variables. Variable basically is a space you can put your value. For example, this is space, okay, in memory, and the cafe is the value. That's it. Space to store your value. Okay, there is different types. Okay, there is an address, strength, bullying, and you teach. This is the biggest one, okay? Okay, address, we start with the address keyword, the name of address, and the address represent an eim address. There is a two types of address external hot address, which means the address of wallet, the honor, the person. And the smart contract address. And why we need the address. Okay? The address is very important in the Eastern Blockchain to get the funds, get the data, sign up to the applications. Many things you can do using the addresses. And the string string. We start with the keyword string, name of the string, and input. So basically, it's just a string. Yeah, just a string. And the Bola, basically, it's true or false. You start with the ball and the name of Bola, and true or false. Okay, integer, the biggest one. U integer variables. So integer, there's two types integer and U integer. Integer accept negatives number, and positives number. And the integer accept just positive. That's it. How to declare, basically, win keyword and max supply equality. The name of the variables and the value. And here is eight, and here is another one. You win 256. This is the number of di byte. So the size and the memory Okay, if the number is small, so this number will take a small size in the memory. If it's big and we don't know how this will take in the memory, we choose a big size for. For example, eight, basically it's eight byte. And 256 byte. Like, what do you think one day is? We don't know. Maybe 1,000, maybe 2000 of second, of course. So that's why we choose the biggest one, which is 256 to store this number. Because if we choose, for example, eight, it byte maybe one day more than that, than the range of you went eight. So there's a problem. Okay, here, with time, the day is 86400. Of second. That's why we started in this one. You went 256. Here's a table of those because it's me, not just eight or 256. Okay, you went 88 byte. The range is 0-255, which means more than that, you have to use another one, more byte. And you went, for example, 16, six bytes, 026 5535. You went 1802802, blah, blah, blah. You went 250 602, the biggest one. Billion or trillion or what is it? Okay, that's it. And sometimes you found you find just wet without specific dvte. So in this case, by default is the biggest one, which is you went 256. And that's it in the wins. I hope this makes sense. It doesn't. We will see more examples in the calculator project, as well as in the classroom project. Okay, please always, always, if you don't know how the number will be. For example, one day, one year, one week. You don't know how second in one week, for example. So always, always choose the biggest size for it. Because if you don't, you choose, for example, a small one, like you went eight. You went 16. We'll take in this, we'll take the max of this, for example, you win 8255, and then the rest of this will gone. This is a problem, a big problem. And a lot of developers do this mistake. So what is a functions? Basically, functions is repeatable task, which means, for example, we want to increment a number. So we create a logic sanctions. And every time we want to increment, just call these sanctions. Okay? That's what is a repeatable task. That's it. So let's move on to the struct of the functions. Okay, basically. So if you have a background in Java, create Python, any programming language. Okay, it's the same. But if you have no it's nothing. Okay, it's fine. We explain everything. Okay? First, we start with the function keywords. Then the name of the functions, then we specific the type, the visibility and the type of the functions. And the last we specific the type of the router. That's so the visibility visibility, basically we decide is this factions, public, which means visible to everyone. Everyone can call it. Contract itself, external contract, another wallet, anyone can call this functions or private, we want to make these functions call inside the contract or in internal, there is a mutual. So first, as I said, can be public, can be used internally and externally. So, for example, it at functions. We can call it internally the functions, the contract, and external. So any contract can call these functions, anyone any wallet can call these functions. Or private private basically can be used within the contact. So if there is a variable, private or functions, which means this variable or functions just visible within the functions. So sorry, within the contact. So the contact itself can call this variable or this functions. Internal. Okay, basically, internal can be used it within the contract, okay, like private and other inheritance contracts, which means within the contract, that's clear, but other inheritance, not other contract, like public. No. Inheritance contract. There is, for example, this basic calculatorre. Okay, this add functions is internal, and advance calculatorre inherits the functions. In basically okay. Explain what is inherent in camulons. Just here, see the advanced calculator, inherit all the logic of the basic calculator. And yeah, so there is a functions here and subtract. Why? Because it's internal. And external can only be accessed from external contract or account. Basically, it's opposite of private. So the ad function, for example, it is external, which means we cannot call it within the contract. Just only external wallet or other conduct. And that's it. So view and per functions, view functions is functions for reading the state into the blockchain, not updating the state. Just to read them. For example, the Git functions, is just for the value of the result. And the result is store into the blockchain. And by calling these functions, we just display the value of result. That's it. And per functions and per functions. Functions is not for reading and not for update dstcs not uplton dstate not reading the value. It's just for some logic, independent of the blockchre like, for example, at functions. Basically, get two variables A and B, and router. They're additional. A plus B. That's it. So A is not storing until the bloing. No, it's locally, not global. That's it. And those functions is for free. The Bloching but updating the state, for example, add some variable to the result. And this update the state of the Bloching. In this case, you have to pay some fee. That's it. Okay, array. So let's say what is an array. Array, basically, it is a list of six. That's it. Like, for example, a list of boxes. Every box has a data and has index, the number. Okay, for example, box one, two, three, four, and so on. And there's an array, for example, NAS, Victoria, Dan and Harry Potter. The more important hair is the index here, okay? The index. This index is useful if you want to access some data into an array. And the Adix always starts with zero, like any programming language. Start with zero, not one, zero. So zero is NAS. One is Victoria and so so how to create an array in SMAT contact. There is a several way to get declared an array in a SMAT contact. First, we start with the type. Then it says string address, bytes, and so on. So in this case, it's wet square bracket, and it's public visibility and, of course, the knee. There's another way if you want to initialize this array with some data say calibraces. One, two, three, list of things. In this case, list of numbers. And of course, you can pix the size. Which means, say, Hey, I want this I want store in this array, 1010 elements in max. That's it. So in the memory, you create an array with ten with ten elements, staffed with zero. Say all element initialized to zero and string five publicly. So this array accept five names. And took it element, an array, you say, there is an array, the values. And here, every values has an index. So basically, put the index of the value in array and you will get the value inside this index. But yes, function, get UN, I Public VU returns Ns returns, array, I R. And if you want to get sorry. Basically, in return, you have to specific calibrass which means I want to get full array and return the N. That's. Otherwise, if you want to add some elements in array. For example, array examples, this is a dynamic array. It can be sized, which means if you don't specify the size, this it will osise every time you add an elements. For example, first, it's empty, so one, one elements, accidually. Add two elements, so the size it's two, three, and so one. That it's opposite if you fix the size. For example, in this case, this is a fixed size array. You win five, public, fixed size. It cannot be resized, which means if this array it's foul for example, there is five elements, you cannot add another one. That's opposite if you declare a dynamic array. And try an element. Basically the name and dot push value. Add a new element to the end of the array. So for example, it's like a pull. There is a body. Push another one. Okay, add another. D tack, tack, tack, and so on. So you cannot add it in center or bottom. And if you want to the function, get dynamic array length, the size, you want to get the size. Basically, the name dot length tin the leg. This is useful for dynamic array, of course, because the fixed array that's fixed so always get five. 5. Build & Deploy a Calculator on Sepolia Testnet: Okay, let's go back to the remix or creating the calculator smart contact and practice all the fundamentals of solidity variables, functions. Yeah, that's it. So let's create a folder, name it. Fundamentos. Inside this, we create a file called calculator, Cal That's it. And we go to the Tab repo for this course. Okay, and use your name Hussein page 2001, the repository ultimate solidity smart contract. Course. And here. Okay. He's exercises, solution, the rhythm. Okay, I highly recommend to create this to boil this calculature before we did. Okay? Where is. He is. Here's exercise and solution. Exercise. Okay, let's copy this Okay. That's it. Okay, make a contra Colt calculator, it is. Create results result variable to store the result. It is as well. It's public and create function to add, okay? Create add functions. Let's create this function. Add you went hinge 566, then when it's external. Okay, let's make it private. Private and result equal result plus nine. Perfect. Here is the first functions. You can create this line, change it like this without repeating the result variable. Just do this plus equal. That's it. Like Python and C plus plus as well. Okay. And here's the compiler. Okay, it's auto compiler. Let's compiling as well, and deploy it. Okay, here's the virtual machine, the account, our contract, deploy. Okay, in the param here, there is our SMAT contract. But just display the result and not the add. Why? Because the result is public and ad is private, which means add functions we can it's usable just within the contract, which means we can call it externally. And by the way, the public variable has Git by default, Git function by default. Okay, and it should by zero. By default is zero. Okay, let's change this one to public or external. Of course, if it's internal as well, we cannot call it externally. So let's market external and copy and redeploy. First, we delete this one, remove it list and deploy. Transactions goes through. Okay, here it is. Okay, check the result first. Mm hm. It's zero by default. Let's at five. Transactions goes through. Expected five. Yeah, it's five. Congratulations. Okay, let's add on the functions. Subtract and multiply. Function, keywords. S. Subtract went 206 external scores, results minus equal. Another one it's multiply. Toxic keywords, Milt, you went 206 name, it'sternal and results multiply equal. The last functions is create a function to get result. But since the result is public, we don't need it because by default, this variable has a get functs. But sometimes we want some variable, we want it to be private, like password, username, owner. So that's why we change this one to private private. And in this case, we need this one Git without any parameter, external. External. Yeah. Okay? We specify the return types. B, we have to return this number. Okay, return. Returns not just return. Returns win en because it's the results. And return award. Ret Add results. That's it. There is a warning. What is it? Is that function state, Vutability can be restricted to view. That's it. Because these functions basically it just to read some data in the block sheheet not to update the data, so we have to market view. And this is not cost any gas. It's free. Reading and blocking? It's free. Least deploy this one. The transaction goes through. Okay. Here is. Our function. First it's at five. That's it. Ts actions goes through. Five. Let's multiply by two. We expected ten. Git. That's it ten minus three. We expected seven. Congratulations. Seven. Now, let's deploy this in SepulaTNt. First, prerequisite. You have to install the metask and stand the extension extension in the crew. As well, you have to create your account and get some thick money SuplaFacet. To do this. Okay, I'm not going to how to create your account and how to stand. Okay, there is a bunch of retrisEplain how. Okay? And Sepolia SepoliaFaucet. To bit some fake money. Okay, so Okay, here is basically copy past your address, and you get zero.05 Sepolieter. And once you have it, let's buter. Okay, Batful, this one is in the ether minute. You have to turn on this show test network and choose SEPolia. Okay, here it is. Okay, let's back to the remix. Let's deploy this in real lock. Check it Mamask. Okay, here's pola here's the network, and there is my others. Look zero X, three, four, four. Look. The same here. It's connected. Maybe I ask you to connect, just confirm the connections, and you get this. Okay, let's deploy this one. Deploy it. We have to pay some fee for deploying some gas, 0.00 17, eight, and so on. Let's confirm this. Pending transaction pen off calculator. Okay, this takes some time to confirm the transaction. Okay 22. As you know blocking is not fast. Okay, O transaction is confirmed. Let's view in Poli scan. Here's this polacanGt and duck it. Okay, here is our contract. Okay, this is just up code. But you byte code because it's not verify yet. Let's verify this functions. Smart contar. Okay, of course, it's just single fi, the version. Okay, our version may be this 1826 plus, which means more than that. Our license open sers ciscopys there. Verify and notable. At this time. Okay verify and publish. That's it. It's fine. Let's take a look. Okay the check mark. Okay, it is. It's the same strive functions. I is ABI. Okay, the red faction Okay, it's gate right functions, which means the updates of the state in the blocking, at functions, multiply, and sutra, subtract, subtract. Okay, let's go back to this one. Okay. Let's add a number four. Okay, our result, what is it? A zero. Okay, I have to confirm transactions because anything you want to do into the blockchain, you have to pay some fee for this one. This is not fast. Transaction is confirmed. Okay. And we get four. When we click the Gt we don't have to pay some fee. Audit it. Yeah, because I double click to the advanctions. And that's it for this time. Graasia. 6. Solidity Intermediate: Mastering Mappings & Structs: Another topic is mappings. So mappings it's amazing things in solidity, and it's cool. I love it personally. So out work basically, okay, pointed to value. That's it. Once you get value, should has the K. Call the K, get the value like student IA. Every student name student has ID, zero, get NAs. Call the mapping one, get Bonny to Larissa. And the cool things here decay is not something for example, here 013. The following one doesn't must be three, for example. No, maybe four to my name. Seeing for example, maybe it's a ten to Victoria, for example. That's different between the mappings and arrays. For example, in this addresses. So that's different between this. Okay? The address pointed to the name. You have the address, you have the name. So to create a mapping in the SMAT contract, we use the mapping keywords and specific type of the key and then the type of the value and the visibility. So here by default is private. But you can market, for example, public or external s. So students the name. So if you want to add an element, basically student specific the key and gate the value, that's it. You want to get some value, basically student address, specifically the K. So you have the value. Okay, another thing is struct. Strack, basically, it's useful if you want to describe something. For example, car a sum. So models so any card has a model year color. In this case, model is Y, years is 2023, the color, sorry. You got di. Okay, Struct. Strat is very useful if you want to describe something. For example, a car. He every car has a models heir and color. This case, for example, Y, 2050 today and blue. And by the way, this is very useful. So for example, if you want to add a student, okay, we see that in the classroom pro. So a student has ID and name, a for example, result and other things present or not, okay, everything you can edit and add the data, how to add data. In this tract and other things useful in this tract, you have the group of variables with different types. For example, string, you went boolean, and so. Okay, here is a Tis la struct. We start with this tract Tisla string model, you went 256, string color and so on. And here's an array of struct. So to add atract Tis la, so the name of the struct, memory, we store this in the memory, not in the storage because it's a lot of space, so that cost a lot of gas. And new Tis la, this is locally, so inside the functions, equal Tisla and models. So decay, the value is models. We get it in the parameter, year, year, color, color, and so on. Then we push the new Tisla to the Tis Ls array. 7. Classroom DApp: Your First Intermediate Solidity Project: Go to the Github repository of this course. Github.com, we've seen pH and 202 001. And then in the repository, and the ultimate solid smart contract course. And then we copy this. Go and create a file, a folder. Let's say mate solidity. Solidity course. No, no. Et's open the base so copy this and get loon So we have. Close this, go to the Remix. Remix. Okay, create a new workspace. Add new workspace. Let's say, a solidity. Course. Course. Create a folder name contact. And then upload a folder. Upload a folder, not file. Where is solidity? The Solid of course, okay? This one. But plot, okay? Is. As exercises as the solutions. Okay, first, exercise. So it's calculator we did this. And create a students this contract. Define student tract with ID, name result, create a mapping, create an array. So let's create a struct. Act. Name it. What? Student? Yes, student. Student student and doing 26, ID, this, then the name string. Name. Result is eight. It's eight. Because result is 0-20. And success or not? Oh, it's a yeah. Success. Warning. Why, why, why. This je data, the name. Okay? You said you constr same name. Okay. Now the warning is good. Okay. Let's add a MPI Mapping QR, MPI. The key what is it? The key basically is ID to the student ID type of uid. Student is struct. Okay, UT six, call ID. T. No, sorry. To students. Students. And let's public or not. Okay, let's say public at this time. Okay, no, ID two. Students. That's it. Okay, let's add an array. Array array of students. So array of this struct. It's student. Okay. Students. Square bracket, size dynamical. We don't fix the size. Because we don't know how many students will be in this class. Let's say it's public and students let's say students is good. Okay, that's it for this exercise. The second exercise, what is it? Okay. The second head is a constructor. Set the owner. Who? Who deploy this? And the honors private. So the exercis add the struck to the array. The struck to the array. Okay, the function add student. Okay, let's add functions student functions. Add student to Marpin. Create a function to students. Basically, create a Function. Get set or ate Studens Ads Okay, ID, name results. First, let's say, ID. You 286 IE. Next string string. In memory. Sydney starting the memory. Okay. It's int, int, okay? At. You know why we market the int because the memory, the result can be negatives. Fortunately, can be negatives. Okay, the result. So result. And, success. So bull Success. Okay, external, of course, none. And external, so little, no, fear, no. Okay. Mm hmm. Students. The clarss did memory. Set use students equal what? Students. Like sorry T and this. So ID ID, the it is ID. The nk As a name kit name value. And sotaRsultR sont. And then Bola, success. Sorry. This is not. I'd like this. First, yeah. Basically, it's just Come on. Perfect. What? Say, not found or not ek. Don't de fire. No fun. Too too dent. So it's my fault. Yeah, I mean. You see, we push this suds cod push students. Student. That's okay. Let's make sure. Okay, and adapt as well in the memory. Sorry, in the mapping. Okay, like this. ID, specific to ID and new student. That's it. That's it this? Caperton arid and biglmt, students or students. What's that? Students, yeah. Okay, that's it. Okay, it's create a function student function. Git students. Perimeters external, of course, and it's a view because we want to read a data in the block chain tool tours the students. Students. Of course, it's memory, starting in memory. Basically, in memory, strings in memory, structs in memory, arrays in memory. Numbers? No, you won't. In this case, you have two options. You can use the student array or the mapping. Let's use mapping. Okay, I T two students, square bracket and specifically I. Tt. Let's compile this one. Okay, you can make this auto compile. So it will compile at the time. It's deployed and see if this is a pin. The transaction goes through. The partner, there's a punches. Okay. Let's say I am number one. My name is RusinaRsult, of course, 20. Success is true. And it transacts. That's it. Okay, let's, let's add another another user. Okay? It's ID ten. It's Bob, for example, ands ten. Okay, two. Yeah. And another one is, let's say, with ID five. Let's say Alice. Sorry, Alice. 24. Add transaction. Okay, my ID is one. It's it Cob? Yeah, that's it. Okay, one, mice, two, and three. Let's Let's bit Ale. To maybe? No, five. Okay, five, Ax, two, and fours. That's great. Okay, in the mapping, for example, let's say Bob. Ten maybe. Huh? Ten? Yeah, it's Bob. Okay, it is Bob and throw student index here to the index. So Bob dex, what is it? My index is zero. The Bob index is one, push, and Alex index is two. So my index is zero S zero. Okay, man. They'd say, two is Alice. We expected Alice. That's it. Alice. He is Alice. Okay, congratulations. 8. Mastering Loops in Solidity (Made Simple): Loops. Loops and the programming. So there is a four. We stopped with the initialization, condon updates, initial condition, updates, and so on. First, we win I equal zero. Then we make sure the condition is through. So I less than five, and we increment this variable. In this case, we increment by one, you can choose a basic by five, I plus five plus ten, as you want. And the logic, we execute this logic. For example, so I equal zero. First, the condition is through, execute this logic here. Then update the I Ecrement by one. Two condition is true. Logic. Equipment, three, through, logic. EguimentFour. Four is less than five. That's it. So execute this logic. And then increment 425. The logic is not true. Is not less than five equal five, so out. And his heritage in the event. For example, function, count up, weight, limit, public per returns, event. So you went sum equal zero, or you wind equal one. The condition by one, two, three, as you want. And the condition, this should be less than limited. Limit, we got it in the parameta. Less or equal, and we increment by one. So then some we add this e to the sum. Until finished until the condition is false, then return to su. Oops. 9. Solidity Loops: Hands-On Exercises for Beginners: Loops to our classroom contract. Okay. And in this exercise, add a function to the success. Okay, we love to check if the student is success or not. Okay? So, function. Okay. Sick says student. So parameters external. Yeah, external. It's a view and returns Rs. A array of struct. Sorry. Student. Student. A array. And m. Sorry. Me Murray. Yep. So first, we stop the length of the student's array. So how many students we have? Okay, 200. Okay. Length equal sudentTt length. That's it. And then we create first. Okay. Let's create the array of students. Another array to store just the student who success, and then return it. Okay? It's student. F it's students, and it's array. Memory. And let's say, success success, Equal new. Okay, the instance of the student ray. Then sorry, the student struct student calibrate, and that's it. This is an error. Okay? Wrong argument, count for the zero argument given but expected one. Okay? In this because this is we start in the memory, not in the storage. So when you sort an array, in the memory, you have to specific the site, especially if it's a strat. If a strat array, you have to specific the size. So which the size in this case is the number of the success student. We don't have how many success. So we create a loop to count those students. So 4156 equal zero have to be less than the length the students array. I say, less than length. And then we increment by one. So we create an account, counter, sorry, counter count. So in the success student, the success is always through. That's okay. Add if statement if students index. Let's say, students zero index zero, Studentx one sus success, the variable of the str successequal, what equal through. So this student is success. Hurl so we increment count plus plus. So and then when the loops is finished, which means the I is equal the length. Why we don't do this equal? Because this I, yeah, equal zero. We initialize by zero. Let's say, the length is, for example, five, we have five student. The I is zero is one is two, is three is four. Okay, four is less than five, but there is a five students. That's why we don't equal list or equal. That's it. So when the account is finished, so we have the number of the success student. So we fix the size of the tract array by discount. That's it. And then we create the same loop, the same But In this time, we add this student. We push it to success array. Okay, like this. So sixes. Sixes to push. Student Hey. It's not a verbal. Instructs students. Outside of storage. Yeah. Okay. We don't create a push. We have to create like this. Equal say students. And then finally this success. Okay, let's compile. Okay. By default, it's autocompiler, so it's compiled successfully. Then let's deploy this contract and say, what happened? Okay, student. Let's add a student like one. Is Bob. Bob is the first one has 1510 children. Sorry. True. Then there is a ten unless let's twin. It's time. It's true, of course. Another one. Five. Let's say, Victoria, Victoria. And let's say it's just four. Sorry. So four, it's four. That's it. Now let's go to get six as people. Okay. Okay, here it is. There is one, Bob, 15, through. Ten, Alice, 20, through. That's it. Okay. We'll create these functions. Congratulations. Okay? This is the exercise. Let's move on to the next step. 10. Solidity Modifiers & Requires Demystified: This is the cool thing. Another cool thing, and the solidity is modifiers. Modifiers basically is a piece of code. Inside of factions. So for example, you have a piece of code. You have to create this code every time in all the factions. And that's Cosa gas, time, and so on. So what you have to do is create a modifier and every time you want to execute this logic, just call this modifier. That's it. Okay, say modifier is functions. You can see that. Okay modifier. Make sure only the owner can code change owner functions. So there is a change owner functions to change the owner. So the owner, who is the owner? There is a constructor. Which means the function you call when you deploy the contract. So once you deploy the contract, the message sender. So who deployed this contra? Me, for example. So I deploy this contract. So I am the messages sender. This sender store in the honor variable. So I am the owner of this SMRT contract. That's it. But there is a function to change the owner. Change the owner. So if someone's see this function, Oh, change the owner. Maybe can call this function with his address, and he will build the owner, the admin of the contract. And that's it's risk. So what we did, what we have to do is make sure these functions should call by the owner only. That's what we add this one modifier, on the honor. So here require message send equal honor. If the message is sender who called this function? Here is a modifier on the honor. This is execute, then the race expli letter. So only honor, I call the functions. I'm not the owner. I called the functions. Then the message is sent. So messageen equal honor, no, I'm not the honor. So reverse, and the honor will be safe. Otherwise, if the owner called these functions, puts a new honor, so he called these functions, this is Sander who is the owner who called these functions. He called the owner, that's true, so change the honor to the new honor. And here is this icon here, this is the wrist code, okay? Execute this first and then the wrist code. I hope this makes sense. If it doesn't, we explain this step by step in the classroom project. We do a lot of this exercise by this. What can you require? We saw it in the modifiers, we explain now. Modifier basically is a condition. If sited, like if segment. Make sure condition is through. If condition is through, continue. Otherwise, revert. That's it. So you create this condition. And the rest SMAT conta do the rest continue or revert based on the conditions. For example, in these functions, there is a MAX permit three functions meant you win 256 amount public. Okay required. Amount is less or equal the MAX permit. If yes, if this condition is true. So the continue, which means you can it the rest of the logic. Which means meant this amount. If it doesn't revert and show this no more than the allowed. For example, I call the factions, and I said the amount two, so two is less than three. Okay, I mean this amount. I, for example, call it again with the FOB for less or equal max permit. No. It's more than three. So the transaction liver and show this one. No more than three, allow it. This is not just option just to know what is the prob in the code. Show it in the concept. And 11. Modifiers & Requires: Practice Challenges in Solidity: Let's add a modifier to our classroom smart contract. Okay, first exercise, create a function to delete student, create only owner modifier, implement the modifier to allow only the owner to call the factits. First, let's create the modifiers. Start with the modifier keyword. And the name on. Sorry. Ana. On Onur.This and here we add the require require statements and come in listens, okay? And do like this. That's it. This icon hair, it's basically the rest of the logic and the faction. Okay, here is a bogic of the code of the modifier here. And then this will tell you the compiler, okay, execute this one first, and then move to the rest code of the function. You can't do like this. Say, Okay, execute the code first of the functions, then execute this one. So this is basically is function logic. Okay. Create a function to delete this the bottom function. Okay? The, the late to the ID, of course, external so we do the same in this one. We compare the ID because we want to delete this on in the just to guess degree, we want to delete this student in the array and in the mapping. First, let's delete this one in the array. To delete some element in array. Basically, move of this to the last element and size the array. So students. Students. But we don't know the ID. We don't know the dex of this student that we have to create a look. Okay. Firstly started the size in length variable equal to students Lock length, then 44206 equal, sorry, equals ten, less than length Sorry, I plus plus plus. If. Now, if the students, A, adds ID equal equal ID equal, equal ID ten students. The last one that last is length, the last index minus one equal. Students. Students. We start this. We move this student to the last element of the array. And then, basically we pop students dot Pop Pop the last elements. And remove it in the mapping. We use the late T word. Okay. I D to mapping and specific the ID. And that's it. So this function is a risk. So if we don't implement the modifier, so anyone can delete any student, anybody. So that's why we have to implement the modifier only owner can call the functions. So in the require require exercise, we add this line, okay? So let's move on to the require require exers. The required exercise. Oh said implement a require modified check if the user if the caller or user okay. He is the owner of the contract. Basically, the only owner. We require message that Sender call these functions is equal to the owner or deploy this contract or not. If yes, move on. Not at revert transactions and log this one. Only owner can call this method. And note. And that's it. Okay, that's before we deploy it. We then the last one and deploy. Okay? Go through here the one. Okay, let's say at say quan Kemi say ten. Let's say zero. Okay. Another one, ten, S, Bob, 20, and three. And we want to delete someone. But make sure. This account, who deployed this contract? So this account, this guy here is the owner of this. So the message sender, the owner is this one. First, let's call this function with this others. Since it is the owner, so the student will delete say one. Transactions goes through, get the student ID one. No, it's a zero, zero faults, which means in the tuple. First, I have the ID zero by name, you see, and through and results. But this okay, let's t's clear he Okay, here. But delete after call this delete and call this function, we get zero and empty, and in the result zero and false which means zero. That's a let's say, Okay, we have another one. It's BG the Bobo, ten, Bob, 20 through. It's delete this car. But it's not the owner who delete this one. No, another one. Say this one. Try to delete Bob. Is that possible? Let's say we expected revert. S it's Bi. Delete. Okay, it's reverse. Why? See why it's reverse. Basically, this action, basically, okay, look at it only owner can call this method. 12. Solidity Events: How They Work & Why They Matter: Is basically a notification from the blocking. And that's very useful. Very, very, very useful. It's a logs to the blocking. Okay, there is a functions. There's a logic, at the end, there's an event from the blockchin. So there is this could execute successfully, then the blocking tells and notifies this function, it's called and execute successfully. Here is a clear example, smart contract. Okay, there is a tabs here, functions one, called the smart contract, and there is a event. So we call dysfunctions, and these functions has a event. So events it's the blockchains. And this app is listings event listener to the blockchain. If anything, update the blockchain. So the block chain will notify the app by this event. For example, there is a function to add a student function in the app. Function to add the student. Okay. This function has a event and ban event student with student ID and the name of the student. That's it. And in coming day, someone some student call these functions. With his information, then and added to the block chin. So the block chain, when he receive this student, he notify the apps, say, Hey, there is a new student added in your app tag. Here is his ID and his name. That's it. So events, create events and events. So in smart contract, we create event like this with the keyword events, the name of the events. And this side, the data, want to log log in, okay? You went to 256 index it data one and string data two. So this index it is useful if you want to filter the data. To accelerate and do easier. No. So that is very useful if you want to test your functions. We see that in the foundry framework. Foundry course, sorry. So functions, function, some function. Okay, public. Dig logic, and then emit this event with the data one and data to emit the name logic, the name of the events and the data. 13. Events in Action: Interactive Solidity Exercises: Let's move to the contract. As exercise events. Okay, events, create an event with four arguments. ID, name result success called student added, and then emit this event in add student function. Create an event with two arguments, ID, name called, student deleted, and emit this one in delayed Student functions. Okay, first let's delete this c. Event keyword. The name student. Okay? Students. Nope. So this one. Okay. And then, first, the ID. The ID is into win 66. ID. N strength. Name. The result ends, not ends. So the result Sixspola. Okay. We want to filter the student, by ID and N, which means this is the most important data. So we make it this one index. And of course, the name, of course, is index. The other is not just. And he said, create another one called student Delay. Okay? As always, even sky words Student deleted. The ID 256 indexed and ID. Then the name string index, that's it and name. So let's emit those events. First, emit this event and add factions. So emit d, and the name of one students students that the first part is ID, so ID and name Kate Nims a guy results results. Then Bola success. Sirk Success. Ad function is this event is is very ab. So this up smart classroom, he listen to the Block list by this event. If somebody called this ad student. So the Bloc chin, say, Hey, classroom, there is another student at his ID, his name, his result, and success or not. Okay, this is the purpose of the events. And, of course, we inmate this one in That's it. Thanks. The name for this one. We will start the name here. Okay? First, save the name to trigger it here. And that's it. This is b, actually. Not like this. It's like this. This is the branch. Store this one and the last one. No. Last one in the actual. Okay, let's com pie. There is a error. What? Added problem. Events. Got expectedly. Ah, I hear you. This semicon? That's it. It's compiled successfully. It's deploy and see the events. Loud or not? It's a. Okay. Let's add someone. Five. My friend Bob ten and through Transactions. It's show her or not? Okay. Here is. Here is in the log. Here is our guy. In there, of course. Yeah, Heats. Even student addts argue. The index is true. So one. But what is the name? Yeah, Herits. Okay. The ID is five above and ten and through. 14. Inheritance & Interfaces: Building Smarter Contracts: Inheritance. So inheritance, here's an example, here's a blue car and truck. So the blue car has some functionality. Drive and reverse and stop. So this is a general car. And but the green car has some additional functionality because most of the time, it can tow and go off road. So but at the same time, has those functionality drive and reverse and stop. So this green car basically it inherits there was functionality in the normal car and add some own functionality. That's it. So let's go ahead and say how this can happen in the SMAT contact. Inherited and smart contract use the is keyword to inherit some contact. For example, there is a contact parent int has this variable parent data. It's public. Child contract inherits from parents. So the contact child is parent, which means inherit the content of the parents and has a variable child data. So and the constructor and the constructor of the child it set the child data. And the inheritance in real world is real contract. The Azuki contact inherit the honorable and ERC 721 A and retrinc card from the imports Okay, there is a open Zeppln library. So the honorable, this is inherit all the contents, the variables and the functions with internal, internal and public visibility. The private cannot be inherits. So let's see how to contract can talk together interactions. Contract interactions. So here is to contract user and G. So this two contact actually has a lot of interactions because the key, the users who play the G. So in the contract users, these functions, create user, the late user, increase level. And in the game contract is a start game and play gay. Basically, the interactions maybe can happen called the struct struct game, this immediately create a user, which means destruct contract called the create user or the game over, for example, the late user or increase user. So this contract, talk to this one user contract. Okay, in smart contracts, for example, is contract A with the data and the set data. And here is a contract, contract B, the interface, we see what is interface layer. So this interface has the same functions, set data and the variable data. It's also a function. So in contract B, there is a constructor sit the interface by the address of the contract A and here and that's how the connections actually create. This is how to create the connections between the contract A and contract B. And basically when this connection is done, so you can call the set data and set the data variable as you want in Contract D, like this. Okay, this function set data in Contact A, you wait to 8,256 data external. Okay, Contract A dot set data, call these functions in the parameter put this data. So this one change by this. So where is the interface? The interface basically is a blue parents. Okay, there is a multiple room. It's play like functions. Okay? So in real world, in the smart contract, here is a contract A, win 256 public and data function set data as we sell and in the interface, his function, see data at in interface, you have to declare a functions without definitions. The k, the parameter, theirs. The same k must be match the name of the functions in the contract A. And this is a variable here. By why we create our functions. Basically because the functions is like a Git functions. And the variable public variable has by default Gitter functions, here it is. Okay. And this is useful when there is a function, for example, there is a contract had a lot of functions. For example, it user data user, stfile change, owner, and so on. And in your contract, you create a contract. You want to you don't want to inherit all those factions. Just you want some of them. Okay? It's a change owner and sit Sitauser. That's it. So you have to create an interface with the same declaration without definition. And in constructor, you declare this interface, and then you sit this interface by the address of that contact. Okay. That's it. So we see this in the exercises. In remix, here is ARC RC 20 tokens, has some functions. These symbols, symbol, name, and signature, total supplier and balance of and transfer, approve and a lot of functions. And I want to create a contract. Okay. Contract Lexi test. Just test. Mm. Okay, Biggs. Le sins bot fryers. Mm hmm. And in my taste contract, I want to use this mint factions, maybe, or name factions. So what I will do, I don't want to use all the functions of the ART. I want just name and mint. So what I will do, create an interface and interface Okay. Interface. Interface, limit ARC to T. And you go to the name of this name name fractions. We'll copy the signature of these fractions. Copy this one. Past public, so cheer to external. As I told you, all the function in interface, it's external. There's view and without definitions. That's it. And functions I won't use it is let's say, let's say mint Mint W is mint. Yeah, this is it is Mint's external internal. Do internal. Change it to external, as I told you. External. And yeah. And I will declare this one. CC 20. Is public and RC Constructor for the address of the RCT. Let's say ARC two equal ARC and change this address to the ARC. And this is how to create the connections. Now, my Airc it's the same address of the ARC I want to interact with. Basically, let's say functions. Name. Let's say string memory. Starting the memory. Well, let's say name. Okay, it's public wary and ARC 20 dot N. No, without parameter. Okay? And just return then. Return. RTs. What? Strain. And the memory sub return Ko That's it. It's mac to you. And that's it. I return the name of the ARC. No, no, no, virtual. Ill to you. Okay, and the MintiaFaction. Fiction Mint. The same here Adessen Okay, ARC 20 Mint count. A not. That's it. This is how to contract interact interact using interface. In 15. Finalizing Classroom DApp: Adding Inheritance & Interfaces: Booking now is a grade parent contract. Created Inherit student contact from Astral, Q. Let's do this. A to inherit and students That's it. And he said, create a function to check if the student is success or not. Okay. Now, the parent has all the functionality of the student. Additionally, he has another function called checks the parent, he want to check if their student is success or not. Let's say function. Okay? Check Success, it's just it's called success, okay? Success, you buy ID. Okay, six force or public, anything? And Richards. What is what? Bula. True or false. So just Bolt. Through tools, sold and it's pure factions because we want to check if true or f. Okay, I IT students IT S says equal true true. Otherwise. As Sorry. As. Return FOS. Yeah. Okay, basically, you can you can just do like this, okay. Return Sorry. Return IT to students ID Taught success. That's it. And this return true or false. That leads sales. This just for No, this is a chick. Not to know just three or four. No, to check if there is success or not. Maybe you can add some logic here, okay? The bonus or can do anything here. But if just return, no, maybe that's it. Okay. I I think it's very good. But, you have the choice. Okay, let's deploy this C chat. Without deleting this one. B. You don't eat this one. The parents. Yeah, the parents. Let's deploy the parent. Okay, now we create a parents contract and inherit the students, then we add additional functions which is successful success. Okay, the parent now he has the ID of their students. So check if true or false. So when we deploy this one, can we still it and redeploy it. Wow, we get all the functionality in the student contract. Additionally, we check successful. Let's add five poke. Always my friend Bob. And then ten. Through. This guy is good. Always through. Then we check five Oh, through. That's it. Add another one. Walls. Okay. It's two less Sorry, Alice, again. Five. And false rest, check the Alice parent to fobs. Okay exercise of this interface, TT T T. Okay, you don't need those Actually, we don't need those. Send it memory. You have to take this one. Okay. Cuz interface over there is in B student create two functions in ad student. So let's go to the ad student He's students. Okay, let's copy this one. And why we need this one just for this type? It because I have this hair and get student. So in this contract is not defined yet, so that's why I copy paste the student struct on the student contact. Okay, here is the function. Okay, let's delete this line by line. Understand how that's going. Okay. First, he said, add add student functions. So we add the function signature. Let's go to student student. He's at functions. Okay, let's copy this. Here, F. And that's it without definition. And G student let's get the signature of G student. Signature only. O here's signature. That's it. I did. So now we have two functions. Head student, get student. And we create, I said, Okay, let's do all these things to answer this line by line. Okay. Okay, create a teacher contact. Here it is. Create a constructor to sit student contract bypassing it as a parameter. Okay, do the globe students. I said it's public and student compact. And constructor constructor, passing the address of student contract and a student student contract equal I student. Convert this to interface, get student. That's it. Now we create the connection between the teacher contract and student contract. Now we have the possibility to call the add function of the student. So we create a function. Let's call it sit my student or add my student as you want, with the same parameter. Okay. You can add any functions as you want. And call this function student contact first. But, but what? Here is the possibility, add functions and get student a function. Okay? Pass the ID, the name, the result, the success. Okay, what is success here, so we add apola Success. That's it. Name results all done. Then another function it's function, get my student. You run ID by ID. It's external force, the view and the return. You have to specific this interface because it will return this Okay. So this is not the students not distract of the student. No, it's distract of the interface. That's why we add this and dot student. Let's take literature. What's. Okay, litre student dot git student and pass the ID. That's it. Okay, contact calls. Let's Let's compile this one. Okay, it's compiled successfully. Check Mark. Let's deploy the Interface first. Hm can't. What? No one can deploy this one. Wow. Okay, we deploy the students first str let's deploy. Okay? This check marks. I love it. And the params our student contract. Then let's deploy this one. It's compiled successfully Deploy. Sorry. We're passing first the address of the student. Okay? And the constructor. Because once you deploy the contract, it's directly called the constructor. So we pass the address of the student, then done. Mm hmm. And that's my student and get student. Contract is deployed, and let's add a student and teacher. True. Bob is my student. Bob results. Let's say ten. Okay, true. That check mats. That's it. Let's say three. My student Alice. Go job Alas 20. True. Let's keep my student two. Here it is two, Bob, ten, through. And what? Yeah, three in Alice. Student Alice. That's it. And the ads of the student Cuts 0d60 CD six a four. That's it for this license. Okay, we finish this one. 16. The Ultimate Solidity Challenge: FundMe DApp: Finally, the fund me project. So this project is more complex, and there's a new concept in this. You have to know before you start this project. Okay, Pike work basically, when you market an address payable, this address is going to accept eight funds. If it doesn't, just declare normal address that cannot be accepted ether. And any iteration to this address, it will be lost. Another thing you can market payable is functions, functions, constructor functions, receive fallback, all those functions, you can market payable. Once you market a function, payable, so these functions can accept Ether, which means when you call these functions, you can send some ether to this function. It's a message that sender, which means hold the address of who these functions. Message dot value is the data, the funds you send with this call, exactly, your call functions, and you send some Ether. So message dot value is the funds you receive you send. So that's why in step three, there is a fun functions allow user to send it. So it is Mr. Dot value in this case. So in functions, there is a step two, owner. Okay, the owner, the one who deployed this contract. Minimum contribution is like a threshd. Okay. The minimum amount you have to send to this contract, the infant functions, there is a user can send it, which means you have to market the functions payable. And the store this amount in a mapping. Mapping with address to amount. Address to, you went, which means the miss GSander who sent who called these functions and sent this eater and the eater who sent the amount, which means innate the name, for example, balance, balance miss sender equal misers dot value. And at the require above. That's it. And scep for declare it withdraw functions. Create the withdraw functions only can only be coll it by the owner, which means only on the fire and recet the contribution. So this withdraw, send all the balance off the contract to the owner, then reset the mapping, reset to zero, which means again, the game is over. So send all the ether in this contract to balance to the owner and rest the balance. And yeah, so how to send all the either of the contract basically is address address this. This is the address of the contract. Address this dot balance. That's it. Like, for example, a user, for example, address user, address dot Balance. Router, the balance of this address. And the CP five modifier, I set and CP six, a contract cannot be accepted. Ether until have two functions, C or fallback functions. Otherwise, the ether will go. So receive it's a trigger that trigger once a contract exit ether, fullback trigger once the contractor accept ether or data. We're explain more two functions in the fund course. To hold Ether. That's it. And S four deploys in Support, a bonus. Okay, or, the top contributor. That's it. Congratulations. A huge thank you to take this course. And I'm so excited to teach you and the first step to jump into the block chain and learn this powerful language. So solidity, okay, I love it personally. It's beautiful language. And more than that, when you learn the solidity, so you have the solidity and taste this code using foundry, this is amaze. This is amazing. So in the next course on the project, I will provide you the solution of this project with additional thing concepts like payable, receive, fallback, as we we add. We know what is a chili, C chili, very and so much more. So, see you in the me project. Again, thank you so much.