Pointers in C

1. Intro of pointers: Hello everyone. In this course we have discussed about pointers in C. So first, we start with understanding pointers in C and then followed by zero point. There are the medical operations and later related to pointers and functions will be discussed. And then combination of strings and pointers. Then it will be point does an ad is combination. Later, we'll be discussing about double pointers and examples related to double pointers and finally, dynamic memory management using pointers. So this is the end. Our curriculum related to pointers. And pointers is the most important topic in C language. Okay? So make use of this pointers. And this will definitely help you to perform well in data structures course. If you're trying to implement in C. 2. Understanding Pointers: Now we'll discuss about the concept of pointers. So first of all, what is meant by a pointer? So generally, goin determines a variable which can store the address of another variable. So point, there is a variable which can store address of another variable. So normal variables cannot hold address of another variable. So that's why we require concept of pointers in order to store the address of another variable. Now, I'll show you an example for this pointer variable and its representation. Now, consider variable n is equal to ten. Okay? So this is a normal variable. Now let me consider a pointer variable in the star d is representing pointer variable. Now I'm storing the address of n into this pointer variable. Okay? So if you focus on this example here, and if I start printing n value, the same n value can be obtained in multiple ways. So e.g. if I write person days DNH, I will be able to display and value. Similarly, I can also use pointer variable star p in order to display value of n so that it is person-based D star p can be used in order to print the value of n. So if you consider this here, n is a variable rate debt. So n is a variable and its corresponding value is. Then star p is equal to address. Often. We are considering Ibis often as a 2000s. And then p is a pointer variable, which is holding address of n and it is 2000. So p is a pointer holding either soften. Now, we are printing the end here. So which means this will display output as a ten. And we're using star P to print, which means how this is going to be evaluated. Star p represents start off bees containing 2000. So start off 2000s, which means the content inside the 2000s memory location. So this star indicates indirection operator, which means it is updating the contents inside this memory location. So content inside of this memory location 2000 is ten. So you're going to ping result as ten here. Now, we can write two different pointers. So while declaring, let us suppose I'm considering different point does here in the star here. So this is a pointer. So I can consider this as a pointer, which can point and in this location. So this is pointer to an end-user memory location. So similarly, I'm considering a float star b. So this is considered as a pointer to a floating point location. So this is pointer to a float. Then car star c. So this is a pointer to character datatype. Okay? So pointer to a memory location. So like this, you can write two different pointers, okay? And you should use in teaser pointer only two point in deserve memory location. Similarly floating point pointer to point the floating point location, and so on like this. Now, let us write a program in order to basically identify the address and our display the content inside the pointer. Okay, so first, I will include the header file here. So this is stdio.h. And inside the main function, I'm considering a variable. Inside the main function. We are considering a variable like number. So let me consider number is equal to some value like 50. Now we can consider a pointer variable into star p. So this is a pointer variable. Now P is equal to address of number, a pointer holding address of another variable. Okay? So now we can print the address of this variable p. Okay? So let me print this address of the variable ISA. So you can use an unsigned int representation. No, okay, percentage. You print this address. And also you can use your value representation. So that is value of b. So our value pointed by p, Okay? So this is value pointed to by pointer p is using person-days D, You can print, which is a star p. So that will print the value that is pointed by point B. Okay? So like this, you can display address and also value using point a b. Okay? Now, let's see what are the advantages of using this pointer. Okay? First of all, you can use this pointer, okay? With the other concepts also. Advantages off point. First one is using pointer. You can reduce code, okay? So this will reduce the code that we're writing. And also it will improve the performance. It will improve performance. And you will see this improvement in performance, especially in C language, while retrieving. Strings are retrieving or accessing trees. Okay? Also one more thing, this pointers are used along with other concepts like structures and functions. So all these topics, so we'll be using this pointers, okay? So it means whenever you want to access the elements of an array, one way is to access through its index. Other ways to access with the help of a pointer which is pointing to the base address of the array. Okay? So now another advantage is generally return statement in C can return only a single value. Whenever you want to return multiple values from a function, you can use a pointer. You can basically return a pointer and using that point there, you can access subsequent memory locations. So I can write here whenever you want to return multiple values or multiple values from a function. Okay? So you're gonna use concept of pointers. And also whenever you use this pointer, so it will allow you to access any memory location in the entire computer. Okay? So this will allow us to access any memory location using pointer. Okay? So now let us write as I'm Bill program using pointers. Okay? So first, I'll perform swapping of two numbers without using third variable, but I will use concept of pointers here. Okay? So first, include the header file here. Inside the main function. First we can consider variables is equal to ten, b is equal to 20. Now, we will consider pointer variables here, star b1, which can hold address of j, n star v2 to find the address of B. Okay? So now you can actually display the content before this wrapping. Before performing swapping, you can display content pointer by P1 and P2. So this can be written as before Swap. Okay? Star p1 equal to using percentage d. Okay? And also I'm considering a star, v2 is equal to percentage slashing. So here I'm writing star b1 content and star. We do condemn them. Okay? Now let us perform swapping, using, okay, without using any third variable directly you can perform with the help of these pointers. So star p1 is equal to star, star p2. Okay? And then here we can write star p2 is equal to star p1 minus p2. And also star p1 is equal to star p1 minus p2. And finally, after swapping, you can display the content like this, print f, the swapping. So now you can display this star b1 content. Also, star p to content that you can display here. So this is going to be star t1, star p2. Okay? So after this sequence of actions, clearly the content of UEN, content of b will be swapped it. So let me show you how this is going to work here. So first, you can show here and it is holding value of initially. Then bees and other variable, which is holding value of 20 initially. Now P1 is a pointer which is holding either Sophie. Let us suppose that the Sophia is 2000s and address of b is 3,000. Okay? So if this is the case, then P1 will be a pointer holding address Sophia, which means 2000 memory location. So P1 will be pointing to this memory location. Now, P2 is another pointer calling address of B, which is 3,000 memory location. And P2 is pointing to this one. Now star p1 is equal to star p, star p two, which means star t1 is pointing basically this location right? Now, this gets updated by adding star P1 contained with a star. We do content. Star P1 content is ten and star P two content is 20. So ten plus 20 will be 30. And that will be stored inside this location, which is pointed by P1. Then star p2 is equal to star p one minus p star p2. So star P1 is contained inside this location, which is 30 minus a star P2, which is 2030 -20 value will be ten, and that will be stored inside this memory location, which is pointed by P2. And finally, star p1 is equal to star p one minus p star p, star P1 is 30, and star p2 is 1030 minus ten will be 20. And that will be stored inside this memory location, which is pointed by p one. So this should be modified it to 20. Finally, we are displaying after swapping up, so star P1 content and then start with to continue. So after swapping star p when content is our 20 and star p2 content is ten. So, but before swapping, you can see star P1 content will be pointing to EA and start P2, which means P2 pointer will be pointing to b, okay? So that is 10.20 initially. But after performing swapping, it is 20.10. Okay? Like this. 3. Pointer Arithmetic: Now we will work on now how pointer increments operation, endpoint or decrement operation is going to work. Okay? So first, consider a variable here, then its value is 50. And I'm considering another point of variable star p here. So P is equal to address of x. Okay? Now you can bring into here the corresponding address for x, which is nothing but P. So print f address off be our address inside IP, address, which is stored inside B. Okay? So you can display it. But I think like this, r of x Caesar. So you can use a percentage you in order to display this address and signed, okay. So B, you can display. Now, let us run this and see the result of asphalt. You can see this is the current address of x is. So this is the present. I press, Okay. Now I want to increment this p by one location, okay? So P equal to P plus one represents incrementing by one memory location. Okay? So address is equal to address plus increment by one memory location. That memory location is equal to size of InDesign. Okay? So P gets incremented y size off in teaser. Okay? Or I can say wanting to sizeof in desert is incremented by one in two sides of in deserve somebody. If I'm taking p plus two, then it represents doing those eyes of InDesign, it will get incremented. So finally, when you want to display here, after incrementation operation, okay. Increment i address is okay. So using person pays you, you can display the address here. Okay? And you can start displaying it. Now, let's run this code and see the reserved. Okay. So if you want, we're going to spin a single line. You're going to observe this is the address of x, right? Okay. And after performing one increment operation, I press is exactly incrementally by four because the four is representing size of one in diesel memory location. So that is why it is incremented by four. Now, if you consider incremented by four, e.g. then this represents B has to be incremented by four in these memory locations, which is nothing but four into size of int teaser, he gets incremented by four into size of int. So after incrementation addresses, you can print here. So let's run this code and see the reserve. So initially this last two digits, you can see the money dollars saved last two digits, 80. And here the last two digits is 96 because the difference is 16. Okay? It clearly indicates we are incrementing current address by four memory locations. And each memory location is equal to this size of int. Size of integer is four bytes. Four into four is equal to 16. That is why it gets incremented by 16. Okay? Now similarly we will consider for a decrement operation, okay? So if you want to consider for decrement operation, okay. So let us modify here to decrement operation. And also here I'll perform p equal to p minus one. So here, P will be decremented by one into size of int. P is equal to p minus one represents P will be decremented by one into sizeof in deserve. After the incrementation, the address will be like this. Okay? So let's run this code and see the reserve. You can observe the address of x is last two characters. You can see Haiti now decremented by one position, which means one memory location equal to the size of integer, which is four bytes. So this should be decremented by four. So value becomes 76 like this. Okay? Then, now e.g. if you want to decrement by four memory locations, then p is equal to P minus four, which means P will be decremented by four input size of int. Size of inducer is going to be four bytes. Four into four is equal to 16. So p should be decremented by 16. Okay? So let's see here. So this is 80 and this is 64, last two digits, okay? Reminding all are same. So it is clearly getting decremented by 16. Okay? So this is how pointer increment and decrement operations will take place. 4. Pointers as parameters to function: Now we are considering a call by reference implementation or passing the address of the variable as a parameter to the function. And you can use to hold the address of the variable. Okay? So let us consider to perform mock sum of two given numbers. So let us consider a comma b are the two variables. So now we can read this variable corresponding values and pass them as parameter to the function. Okay? So now I'll prompt the user here to enter any two values. And using scanner function, we can read those values like person-days, the person takes the address of a comma b. Okay? Now, we need to pass these variables as parameter to a function so that it will compute sum of these two numbers. So I'll consider find summons the name of the function, passing two variables and preserve a coma address of the S parameters. This function, I'm using return type as wide so that I can display the result to within this function. Using pointer. We are performing here star PTR one comma into star PTR too. So within this function, we can compute a result by adding the content which is pointed by PT R1 and R2. Because PTR one will be holding address of a and P DR2 will be holding the address of B. Okay? Now consider another variable called aureus, which is a result variable. Now aureus is equal to star p d R1 plus star PTR two. And finally, you can print the result. So result of adding Easter Sunday is the slashing and you can display RES value. Okay? So let's run this code and silver reserves enter any two values, 12.23. And you're going to observe the dessert after adding is 35 plus 23s. Define. So this is how you can pass the address of the variable as parameter to the function and compute and display the result. So the under computation is done with the help of this pointer variables which are currently holding the address of the variables which are passive in the main function. Okay? So this is also as an example of call by reference implementation. And this is also considered as using pointers as parameter to a function. Okay? 5. Pointer to a function: Now let us consider our concept of pointer to a function. Okay? So you can also use a pointer in order to point IF function. So just like how we have used a pointer to pointer variable, similar to that, you can also use a pointer to point IF function in C. Okay? So and also declaring the pointer variable is similar to function declaration. So let me show you with an example here. I want to basically implement main function right now. Okay? So inside this main function, I will consider a variable called Reserved variable. And this point that I want to point star PTR, I wanted to point to another function. So let us suppose the function declaration is addition initially is the name of the function, and this is the function prototype declaration. Okay, so now how do you declare a pointer which is pointing to a function? So it should be declared just like how we write the function. Okay? So star PTR, okay? Like this. Now you can use this PDR 2-point I press of another function which is VTR is equal to I dress or function name is addition. Okay? Now, we need to extract the reserve. Reserve is equal to, okay? So you're basically calling the function. Generally you will call the function and its corresponding results should be stored inside a variable result. But right now, you're going to absorb a PDR is the pointer which is pointing to the function called addition. So writing this is nothing but the calling a function called edition. Okay? So this is equivalent to calling an addition function here. So now, once you get the desert, you can display that preserved. Okay? So this sum is using person-based should be. You can display the result. Now let us implement this addition function. Okay? So here, as I have already declared the function prototype or declaration I can implement here. Now, inside this function, I'll basically read the two variables and the corresponding values. I'm going to perform some. Okay? So those two variables are in B, okay? And I'll clearly prompt the user to enter any two values. And using scan f statement, you can read this. Person days be person-days. I press Off a comma b. And finally you can return a plus b reserved. Finally, you can return a plus b deserved it. So let's execute and see the reserve to enter any two values I'm entering. First value is in, an x value is 20, and you can see the result, the sum is 30. So how this is obtained is clearly, instead of calling this addition function directly, we are using a pointer to hold the address of the addition function. Okay? Using pointer, we are calling this function and extracting the reserve and storing it inside a variable called result. And then we're displaying that. Okay? So this is the concept of pointer to a function in C. And it will produce character reserves. Just like this, you can enter any two values, like to six and it will produce the result as eight. Okay? 6. Accessing string using pointers: Now in this example, we'll see how to access a string using pointer. Okay? So consider the main function. Inside this main function, you are considering a character which is a string. So this is STR off is equal to hello. Hello is this string. Now also consider star PDR. Pdr is the pointer pointing to the base address of the string, which means always remember string name is representing the address itself, our base address of the string. So you need to use like this p d or equal to USTR, which means directly, USTR is indicating the address itself, so PDR will be holding that address. Now using PDR, you can display the content which is pointed by this VTR. Okay? So using while loop, you can display this content. While star PTR not equal to null character. Star PTR not equal to null character. Then in that case, you can bring star PTR content. So percentage d star PTR. And you can use PDR to increment to the next position. So this is going to be PTR plus plus increments by one position and move to the next location and start printing that contender and move to the next location like this. So let's run this code and see the reserve. Okay, here, you should use person-days. See, otherwise. It will display its corresponding ascii value. Okay? So person-days see to get the character exactly. So same string, hello is displayed. Let us suppose you have a string like hello space world. You will be able to access hello space world using this code. You can see the reserve Hello Alice displayed. This way. You can access the contents of the string with the help of a pointer variable. 7. String Comparision using Pointers: It's now we will implement string comparison using a concept of pointers. So let us consider a STR r1 contains hello and STR contains void. Now I want to perform a comparison between these two strings with them pointers. So let me consider an integer variable which can hold the comparative reserve. And I'll call the function, which is my STR CMP function, bypassing STR one and STR QS parameters to this function. And finally, I will display here, reserve that string. Comparison. Reserve Is person, is B. So we're going to display result here. Okay? Now, let us implement this function which is my STR CMP function. So using pointers, let me consider. One is the pointer to point to string 1.2 as the pointer to point string too. Okay? So how will you get the string comparison Brazil? It is simple where you have to basically compare two strings and identify the ascii value difference between the first non-matching character. Okay? So for this purpose, I compare the two strings as long as they are equal with the help of while loop. Okay? First, let us suppose a star is, S1 is equal to star is to start, S1 is equal to star is two. And also you need to check here. Star is S1 should be not equal to null. Okay? So this is not equal to null. Or I can say null character. Anything is fine. So either this is not null. Our star is two is not equal to null. Okay? So the first condition is the character located in sites STR one is equal to character located in STR two, which is pointer by S1 and S2 pointer. And also consider s1, whatever s1 point that is pointing is not equal to null. Or S2 pointing is not equal to null. In that case only we will proceed further. Okay? So in that case we will increment the S1 to the next position and also as two to the next position. So S1 will be incremented and S2 will be incremented. Now, here, I will return the difference between S1 and S2. So here, return star is S1 minus a star is two. So that will give you the difference between star s1 and start as to which is nothing but non-matching characters, corresponding difference. Okay? So either s1 is not null or S2 is not null, then only this will, this particular loop is run, running, okay? So overall, you can see when this condition is true, then only it will work, right? So this must be true and also this must be true. So which means the characters should be matching at the same time. Any one of this string is not reaching null. Okay? So point, you can see S1, pointer and pointer incrementing to the next positions. And whenever you find that there is a non-matching character or both are reaching to null. In such cases, you have to immediately find the difference between these characters, okay? So those non-matching characters. Let's run this code and see reserved. You can see string comparison result is -15 because we are comparing hello with world. First two non-matching character is directly hit U and W itself. Okay? So h minus w, The difference is clearly 15 characters difference. And this H comes first when compared to w. That's why h minus w will lead to -15. So the result is shown as -15. Okay? So let us suppose I want to modify this string like x, y zed. And also this says x, x, z. Now let's run this code and see the reserved y minus x is going to produce one. Okay? Like this. Suppose if I'm giving this as x, x, z, and this is x, y, z. In such case, you will get a result as minus one. Suppose if the modal strings are equal, basically x, y, z and x y, z. In such case you will get result as zero. Okay? 8. String Concatenation using pointers: Now, in this video, I'll show you how to perform string concatenation operation with the help of pointers. So I lose concept of pointers to perform this string concatenation operation. Also, I'll perform this string concatenation in a separate function. Okay? So let me write here string concatenation using pointers. So first I will include the header file. Yes, TDI would catch. Now inside the main function. Consider a couple of strings here. So consider STR one equal to hello and STR equal to void. So consider a bigger size for STR one because I want to concatenate inside STR one. So that's right. We're going to consider STR one is our 20 e.g. and then I'm concatenating the content of SGR, STR one. So let me call it function here, which is my STR CAP function. And I'll pass STR one karma STR to as parameters to this function. And later, we can display STR one content. Okay? So string one, nice person days, yes. You can display as DR1 contents. Now let us implement this My STR CAD function. So let us consider this function implementation. Where I consider a couple of pointers Less. Let us suppose I am considering star is two and star is S1 here. Inside my STR CAD. Now I want to move to the end of the string that you can observe for STR one, I am using a stew as the pointer. Okay? So first you have to use this S22 I trade to the end of this string. Using while loop you can hydrate this star S2 is not equal to null character. So in that case you simply increment this is two by one. And now you need to check whether this one is okay. So first, Yes, When he's already pointing those string two right there. So you have to access character-by-character and append it to this string, STR one string which is pointed by S2. So this can be done like this using while loop. I'm going to check like this. Star is S1 is not equal to null character. If this condition is true, then we can copy and also increment. In a single statement. I'm coping like this. S star is two plus plus is equal to star s1 plus, plus. Okay? And finally, after entire coping is completed, then you just need to explicitly place a null character. So which can be star is two is equal to null character. Okay? Like this. Now, let us run this code and see the reserved. And we're going to see the updated string is hello world. String one is hello word. So initially string one contains only Hello, string two contains world. Now after performing string concatenation operation, which is implemented using pointers with string1 is pointed by character pointer S2, and string two is pointer by character pointer S1. For us, we have moved to the end of string one with the help of stupendous. And later we started coping with helper for s1 point character-by-character into the location whereas two is pointing. So finally, we are assigning a status to equal to null character, which means we are indicating the null character at the end of the string after concatenation. So now we are able to access the content of STR one, which contains concatenated result of STI R1 and R2. So this is how it will work. 9. Finding Length of the string using pointers: Now let us compute length of this string using pointer variable. So you can observe I have taken a string name as HelloWorld and star. Ptr is the pointer variable is pointing to the base address, which is STR. Now, you can start counting the number of characters inside this string, which is the length of this string. You can consider n equal to zero representing the length of the string. Now, using while loop, you can either treat here while star PTR not equal to null character. So if this is the case, then you can increment the length of the string, okay? Because you have to count each and every character inside the string. So alien plus, plus, and also Moody's PDR to the next position. After counting the first character, it has to go to the second character. Okay? So once all the characters are counted, you can display the length of the string here. So length of string, ease. Person days should be alien. Using alien a variable, you can display the length of the string. Now, let's run this code and see the length of the string is 11. So clearly there are a total 11 characters in this string, including spacer, total lemon characters are there. This is how you can find the length of the string. Okay? You can also try passing this STRS parameter to the function and identify the length of the string and another function. So let me show you here. So PTR is equal to STR. And we're going to implement a separate function to find the length of the string. So I would write my own function, which is the MISTRA alien. And here I'll use the pointer variable like star, PTR pointer. And you're going to see if PDR is equal to STR. Here. Since we're passing character pointer, this must be character pointer as well. Okay? So the idea is to just consider a variable called EN, okay? To find the length of the string. And this equal to, call this function My STR alien function. And pass this STR as parameter. Okay? Because everything we are computing in the other function, you don't need to take this pointer at all in this function. So again, this equal to my STR allele and off STR, I'm passing a STRS parameter to my STR Len function. And finally, you can display the length of this string here. Print f string length. String length is here. You can display length of the string using variable EN. And you have to implement this MISTRA LEN function. So with the help of pointers, that is character pointer. So let us consider another character pointer like car star m. Okay? And initially I'll consider temp is equal to PTR mode, this PTR and temper pointing to the base address of the string STR. Now, I would like to only the temple point. So while this star m is not equal to null character, we can treat that here. So you can move this temp pointer to the next position. Okay? So since only one line, you can skip this M plus, plus. Okay? Once the star temp is pointing to null character, then finally, you can return here. **** minus PTR. As we know, character location is going to occupy only a one byte. Okay? So temp is now pointing to the last location in the string, and PDR is already pointing to the first location in the string. So it will give you the difference, right? And that will become the length of the string. Okay? So let's run this code and see the result. String length is less than. So. This is a string, right? Hello space, world, total 11 characters are there. And we are able to get the same result. Okay? So this is how you can pass a string name as parameter to the function and use character pointer to point to that string and compute the length of the string here. Okay. 10. Pointers & 1D arrays: Now we'll discuss about pointers and one-dimensional add is. If you observe this concept of pointers and one-dimensional arrays. First I'll show you how this pointer can be used to access the content inside this one-dimensional array. Okay? So whenever write it clearer. Now, let us suppose in the age of five. Okay? So you're going to observe there will be phi contiguous memory locations. So you can see this is an RNA called yay. Okay. This is integrating the very first location, the knee off one. This is your 234 like this. Now using pointer, you can access content inside each of these locations. Okay? Let us suppose I want to store at compile time the list of values inside this array. Suppose if I store like this, 102-030-4050. So in this case, these are the values that are stored and will be stored here. 20 is stored here, 30 is stored here, 40 is stored here, and 50 will be stored here. Now, consider the base address. Let us suppose this is the base address of the array, which is 2000s. And this is 2004, as in desert is occupying four bytes. This is 2008, this is 2012, and this is 2016. These are the corresponding addresses. Now, using pointer, we can actually point to the base address of the entire array. So this can be indicated, let us suppose using a pointer variable. So consider in the star PTR. So PTR is the pointer variable I'm using. This PDR can point to the base address of the array, address of a of zero, e.g. you can store like this address of a of zero. Or simply EH, selfie is representing the base address. Okay? So now when you perform this action, PDR equal to address off here of zero, it is going to consider this pointer variable, corridor, PTR. And it will store the address of the main centers of the entire array. Are you off zero corresponding address, which is a 2000s. This will store 2000. Npr will be pointing to this memory location. Okay? Now using PTR, you can access each and every element inside the array. So for this purpose, I will take another loop variable called i. So I'll write a sample for loop to create an access each and every element inside this array with the help of a pointer. So I is equal to zero. And then consider I less than five because there are five elements inside the array. Now, using print f statement, we can display each of these elements. Print f, percentage d slash t. Now I display PTR is pointing to this location. How can I get the element? So when I mean PTR, I get 2000s. When I write a star PTR, I'll get content inside 2000 memory location, which is ten. And after that I want to access this content called 20, then 30, then 40, then 50, like this. So in such case I value, we are going to use that updated I value right? Star off PTR less. I start off with DR. place. So this I value will be I treated starting from I equal to zero up to I is equal to four. And this is a star of PTR place I. So when I start off PDR plus I, this is actually equivalent to, okay. So you're going to observe star off VTR less than zero. This is equivalent to writing u of zero. Okay? When you consider I is equal to one, this will become star of PTR plus one. And this will be equivalent to one. Okay? And writing star of PTR L2, where I is equal to two, in this case it means equal energy to lay off two and so on. Similarly, you can see here star of PTR plus four. This is nothing but four, okay? Like this. And if there are n number of elements stored inside the array. So in that case, you can simply write star off VTR less. En is equal to e off. Okay? Or it can be K simply PDR plus k is equal to a of k like that. Okay? So now let me basically read the entire content of the array with the help of pointers itself and display the content of the one-dimensional array. So first, take the header file. And inside the main function, I'm going to consider an array here. Okay? So consider a raise e off 20 e.g. and I'm using two variables in non dye inside and you can store the number of elements or length of the array. For this purpose, you can bring to this statement. Number of elements are simply enter size. So using scan f statement, you can read that particular size into variable quality and address often. Now, we're going to prompt the user with Scully to lead our enter those many elements. Here you can ask ender percent is the elements, which means n elements. We're asking the user to enter. Now using for loop, I'm going to axis, okay? So directly here, I'm not even taking any point using airy only I'm accessing here. I equal to zero, I less than n I plus plus. Now we can store using scan f statement. So this is scan f person days of the year plus i. Okay? So we're storing inside the array. Now when you want to display similarly using print f, You can just say displaying elements of array. And after that, you can simply use this for loop. I equal to zero I less than n I plus plus. And using print f statement, you can display like this person is D star of a plus i content inside that particular address is obtained. You can close this main function. So this code is basically for reading with the concept of pointers. And this is using the concept of pointers. We are displaying the content of one-dimensional array. Or you can directly take another pointer and point to this base address of the array and start titrating. Okay? So either way you can do it. So let me show you with an example where I will modify and show you different ways. So that is considered accessing the content of the array. Here. In the main function. I'm going to add it here. Let me see off 20 comma n comma i. Now I'll prompt the user to basically into n value. So once you enter in values using scanner statement, you can read it into variable in. Okay. So later, you can prompt the user to person D is the values. And exactly you need to get even number of values. Okay? Then using for loop, you can start storing these values inside this array with the notation of pointer notation. So using scan f statement, you can write like this person days of d. Simply a plus I. This denotes here a plus I is nothing but address of address off your file. So you can see a plus cy is equivalent to phi. Okay? Just like this. Now, here. Similarly, I want to display this content. So using printer, you can just display array elements. And again, using for loop here. And instead of scanner, you have to use printf statement to display the content. Deaf person days, the star of a plus I. This will give you the content inside that memory location. And if I write like this, this represents EOF means it is equivalent to star of a plus I. Start off a plus right, is equivalent to a or PHI. So let's run this code and see the result. Okay? So here we have to use a semicolon. Enter n value, I'm entering in values five. Now it will ask you to enter five values. Let us suppose 1020304050 are the values I have given. You can see the same values are getting printed, okay? So I'll use here a person days, four days so that there will be some space while displaying the elements. So this time I have entered a 6,000 value. So consider different values like 12, 304-203-5663 for P2. Okay, these are the six elements I have given. Now you can see displaying our elements 1234, 2035, 0660, 3402. Same. So instead of writing star of a plus i, okay, you can directly write e of I. This is a general notation where we have used while working with that is okay, So address off, you're off. Let me show you here in a race, this is the notation we have used. Suppose n values for 122,345.56, see the same value, so the spread. Okay? Now, instead of using the acronym directly, you can also use pointers. A great point there, an integer pointer. Okay? You can use this PTR to point. I dress off the off zero. Now using pointer, you can access everything here. Simply write PTR plus I. And here instead of writing your file, you can write start off PDR. Bless. Okay. So this will also work. This time I have given n value is five. Elements are n 2030, 40.50. Again, see displaying our elements 102-030-4050, like this. Okay? 11. Pointers & 2D arrays: In this video, we will discuss about how to access a two-dimensional array using concept of pointers. So this is pointers and 2D arrays. That is two-dimensional arrays. Okay? Now, if you consider here, generally, NRA. Let us suppose I'm considering an array which is a two-dimensional array, like 23. This denotes mescaline Eric, or which contains how many Rosa? So there are two rows and three columns. That are two rows and three columns. So row number, and then these are all column numbers, right? Okay? So if you look at these locations, this is representing your office zero-zero, okay? And this is representing your 01. This is the all zero too. This is representing a 0 of 10, and this is your 11. This is the old 12, like this. Now, when I want to store a value in this particular location, we generally write address, so you-all for zero-zero. Okay? This is clearly equivalent to writing start off year plus zero plus zero using pointers, okay? Suppose if you want to display this contender, that is the off with zeros, zero content you want to display using printf statement. Then its equivalent is in pointers. It is a star off, start off EA plus zero plus zero. Okay? So these two are equivalent. Similarly, these two are equivalent. Now, let me show you here clearly. When I mean the representation as suppose is the Adi, okay? In the, off to three, the same attic. Or does this year represents okay? So then I mean here, it actually represents a pointer to the first row. Okay? So this is representing pointer to first row directly. So when I write k plus i, it represents a pointer to the IEP through, okay? Pointer to I know e.g. if I write star off here plus I. And this is representing pointer to the first element in the eye and through, okay? Very first element in I, throw somebody if I write, start off here, plus I plus j. So this represents a pointer to the I delivered in the eye. Okay? Pointer to the element. Okay? So I know when I mean, start off, start off it plus I plus j. This represents the value that is stored inside IJ location, okay? So which is nothing but the value stored at, okay? In added representation, you can see value stored at a of I j location. This is the meaning here. Okay? So now whenever we want to basically read the elements into a two-dimensional array, okay? And also display the elements from the two-dimensional array. So we can write like this. First, I will include the respective header file stdio.h. Now using this main function, okay. So far, so you can see there are and add eight quarterly x and its size is five-by-five. Okay? And also I consider p, q for indicating the row size and column Sicer INJ or the loop variables here. So now first we will print or display the user to enter the order of matrix and the order of matrix. So you need to read this order of the matrix. Person, basically person-days, the address of p and address of q, because p is representing the row size and q is representing the column size here. Then you can prompt the user to enter order of matrix that the corresponding elements, number of elements is equal to pin to Q, right? So I can write interpersonal elements here. And the number of elements should be between two Q number of elements. Okay? So once users started entering those many aluminums, you can read them inside the array. Using a for loop. I equal to zero to I iterate through all the row. So i less than p I plus, plus. And similarly, for j equal to zero, j less than Q, j plus plus. Now, using this scan of statement, we can read by writing like this percentage d. So generally nowadays you will write address off you off or whatever name is here I have considered are in MS. Excel, so you have to write our dress off. Off. I j. We have already discussed here. I dress off EX saw phi j is nothing but you have to write like this, okay? That is a star of x plus I plus j. So using pointers, it's equivalent is start off x plus I plus G. Like this. Now this is using a scan f statement we are reading. And later we're going to display the content here. So in the form of a matrix, which is a two-dimensional array, that is matrix content that you can display like this. So while displaying, again, you can use this for loop I equal to zero I less than p I plus, plus. This is indicating the row. And then column-wise, for j equal to zero, j less than Q j plus plus. Now we can print like this, print f person there should be. This is printing purpose. You have to write star of star off we explicitly plus j, okay? Because this is equivalent to writing simply X of IJ. Okay? So for two-dimensions, you require two stars to access the content inside that location. Then you have to use new line so that after every row it will move to the new line to print the next line and then close this. So this is the format that we use here in order to basically read and write contents of the two-dimensional array with the help of pointers. Okay? Now, let us implement this and see if there are any changes needed. So here for styling the respect you header file stdio.h. And inside this main function, consider a sample array, which is a two-dimensional array. Okay? Consider there are two rows and three columns. And I'll go for compile them initialization for the first time, okay. 456. And I'll just display these elements using pointers. Okay? I is a loop variable and Jason loop variable. Now, using for loop, we can I treat like this, I equal to zero, I less than two, I plus, plus. Okay? Because he is representing the row size. Now consider column size three. So J equal to zero, j less than three, j plus, plus. You can print this here. Print f. Usually we'll write person, they should be. Okay. I, j notation. In order to display the content in the form of a matrix. So line by line. Okay? So if you want, I can write a message. Tricks. You can display the metrics content. Now, let's execute this and see them. So in order to display basically elements with some space after it, you have to write person-days WD format, where w is representing the victim. So I have used up three characters. One character will be printed and remaining two characters will act as spaces. So this is how we generally printer a two-dimensional Adi. Now I'll replace this with its corresponding notation using pointers, that is a star off, start off E a plus I plus j. Okay? Now let's run this code and see the result. You can see matrixes, so there are two rows and three columns. Okay? The same matrix is displayed using this lesson. So as I told, there are two indices, because this is a two-dimensional array. To access the content, you will have to use a double star here, that is a one star and another star sub l. If you're writing only a single star, then I'll show you what happens here. If you're not writing to stars and writing a single star like this, then you will end up printing all the addresses, okay? Suppose there are, since it is art brush, you can see the result is this one. These are all addresses that are allocated for this particular matrix. Okay? So if you want to access the content inside it, you have to use another star here. Okay? So it is completely close rate. Now let's run and see if you can see like this you will get. Now, let us suppose if I wanted to basically read the content of the matrix, then in that case, at runtime, you can store like this, e.g. this is something like ten here, okay? And also this is another 1010 by ten two-dimensional Mary I'm taking. But you can prompt the user to basically enter the order of the matrix. Okay? So printers order often breaks. Okay? Now you have to read that particular matrix that is person DSD, person-based, the address of p comma address of q. Okay? Later you need to prompt the user to enter those many elements, like endo percent is the elements. Okay? So which means exactly into q elements. Once the user starts entering Boltzmann elements, you can start reading them. I less than p, because p is representing the row size. And j equal to zero, j less than Q, j plus, plus because j is representing the column that is a. Okay? So q is representing this size of the column. And now I use this scanner statement in order to read these elements. So person-days be okay. As the address I have already shown you, this is representing clearly the address, right? So you have to store the element inside of that address and then you can access it. So again, since we have taken a p by q as the order, you have to use that p by q order in order to display these elements. So let's run this code and see the result. Enter order of the matrix, e.g. order of the matrix is three by three. It will prompt you to enter nine elements. The elements are 123-45-6789, okay? And you can now see the matrix is 123-45-6789, like this. Okay? So this is how you can use concept of pointers to access and store it in the two-dimensional array. Okay? 12. Double Pointers: Next one is double pointer, or a pointer to a pointer in C. Okay? So you're gonna, um, so here's a pointer to a pointer or double pointer. So the general definition of a pointer to a pointer or a double pointer is a pointer pointing to address off another pointer, okay. So is considered as point directly at binder or double pointer. So let me write here Winder cooling address off another pointer calling our dress off. And other pointer is called point. We're pointing to. You scored pointer to a pointer or double pointer. So what is the general syntax of such double pointer? Pointer to a pointer? So let me denote this index sulfate. So the general syntax will be consider any data type, but it can mean desert or character or float or double anything. So datatype but star, star, pointer to a pointer. So this variable name can be anything, but you have to consider two stars, which represents a double pointer, pointer to a pointer. Now let's see an example of how to work with variables. So, okay, pointer to a pointer inside the main function. Okay? So first, after including the header file. And inside the main function, I'm considering like this is available, which is holding. And also I'm considering a single pointer or normal binder. And this is a double pointer or a pointer to a pointer. Okay? So first I will store the address of a to point B and address of b into pointer pb. Okay? Now, you can display the content using Star KPI or double star p here. So I'll show you whenever you want to display the value of k, you can write like this. Or you can also make use of a pointer variable, which is a star p. You have another way of accessing the same content. Both pointer to a pointer that is present is d double star p. Okay? So using which you can access content inside the memory location. Yeah. Okay. So let us see here how this is going to work. First of all, is a variable and it is holding the value of ten. Okay? And P is a point. The ruling Agisoft, which means consider are there Sophia is a 2000 memory location and the fees if pointer holding address Sophie Sofia is a 2000 and p is pointing to this memory location. Okay? No, every pointer will also have an interest rate because that will be stored in some memory location. And memory location will have an address. Let us suppose 3,000 is the address of pointer variable p. Now, this pointer variable corresponding address will be stored inside another point, which is a pointer to a pointer. So this is representing pointer to a pointer and we'll be holding address of p. So 3,000. You can see BB pointer to a pointer is holding address of p. Okay? Now when you start printing value of E, So this will give you result as a ten. Okay? Then when you start printing star p. So let's see how this is going to be evaluated. Star p represents a star. B means 2000s. Content inside Pluto's and memory location will be displayed, which is ten again. Okay. Now let's see how this pointer to a pointer will be evaluated. So here we are printing clearly double star BP, which can be evaluated as a star. Star. Pb content is 3,000. From here to here, content inside 3,000 memory location. So what is the content inside 3,000 memory location here? So content inside 3,000 memory location is clearly 2000s. So start off 2000s, which means content inside memory location, The answer is ten. So to display the same, then you can perform these actions. So these are the multiple ways to access the same content. Which means the same content can be modified either directly using the variable or using a pointer variable, or using a double pointer or a pointer to a pointer. Like this. You can write a program which makes use of a pointer to a pointer and also a single pointer. So now let me show you an example, okay, for this pointer to a pointer. So far as to reconsider the header file. Then inside the main function. So let us consider a variable like E is equal to ten and star, double star is pointer to a pointer. Now I use P is equal to I dress off. And another one is Pb right there. So Pb is holding the address of p. Okay? Now in order to display value of Yi, you can access in multiple ways. Here. I'm using new line, okay? Directly, you can use variable yet. Okay? So here I'll write that a is equal to. Now similarly, I want to access with the help of a single pointer, which is a star p, star p corresponding content. I'm going to display here. And after this, we need to print the double star p. Star p is equal to percent is the slashing double star p. Okay? So now let us run this code and see the reserve. So here invalid type argument of unitary operator star have in-depth. So let us declare like this. Okay? So consider a double star B, okay? And this is single star p. So which means value stored inside this, right? Okay? And he just showing in nine line here. Okay? So one thing I do here, this is int star p is equal to, and this is e1 star, star p equal to. Invalidate a type of argument or funerary star. Okay? Sorry, here. The problem is, here we have already taken PSD single-point. They're under double star P. Double star p, which is the name of the double pointer. So we have written a single p. That's right. It's showing that it's basically PPE is the name of the double pointer we have taken. We have to use the same name. You can see that it's earning a is equal to ten star p is equal to ten. Double star p is equal to ten. Okay? So like this, you can display the content, okay? 13. Example program in Double pointers: Let me consider an example which involves a single pointer and double pointer. Okay? So let us consider X is equal to ten. And I'll consider our different variables like star p is a single pointer and double star PTR is a pointer to a pointer. Okay? So here I consider p is equal to either Sophie Excel. Nper is equal to address of p. Okay? So which means if you are performing any action through pointer p or through double pointer PTR. So that will affect the memory location which is allocated for variables except the content inside variable x gets updated. So let us suppose I am performing double star PDR is equal to two, okay? Single star p plus 25. Okay? Now finally, when you print the value of x, this will affect the value of x or zero value of x. Okay? So let me show you the result. The result should be 35, okay? So why 35 is the answer? Because you can observe double star PTR is actually representing the content inside variable X. Now this is going to be here, star p plus 25. So p is pointing to a memory location x and it contains value ten. So ten plus 2510 plus 25 value will be 35. So PTR is the pointer which is pointing to that memory location and its value gets updated to 35. And later we are displaying x value. So right now the x value is updated to 35, which means this is the same location where we are referring to x and also equal to star p. So all these are all equal to 35, x is equal to 35. Startup is that if I double star PDR is 35. So this is how you can manipulate the content in a memory location using a single pointer or double pointer. Like this. 14. Dynamic Memory & Functions: In this session, we will discuss about dynamic memory management. Okay? So this is also termed as dynamic memory allocation. So generally, what is the problem with this static memory allocation? Okay? So if you consider, in C language, we often use this static memory location. An example for our static or fixed memory location is, let us suppose you are having declared in d of five and then semicolon. So this actually represents, it is going to allocate five contiguous memory locations. You'll allocate five contiguous memory locations just like this, 1,234.5. Now, this location is representing a of zero. So this is your f1. This is the off to three. And this is here for like this, there will be five contiguous memory locations. Now, the problem with the static memory location, so this is considered as a static or fixed to the way of allocating memory. So the problem here is if you want to store ten elements, you cannot store because the memory is allocated only four or five contiguous elements. If you are using only two elements, then reminding memory location, that is five minus two equal to three locations will be clearly wasted. Memory is visceral for three locations. Okay? So this is a problem with static or fixed memory location. Okay? Now, to overcome this, in C, we have dynamic memory location where you supply value dynamically. And the memory is allocated based on the value that you have supplied. Okay? So e.g. you are taking n value at runtime and it can create the n contiguous memory locations as per your requirement. Okay? So that is considered as our dynamic memory allocation. Here. There are different dynamic memory allocation functions available in C. Okay? So those functions are first one is malloc function. So this is a malloc function. And using malloc generally we allocate whatever requested size of whites by the user. Those many bytes of memory will be allocated and the pointer will be pointing to the first byte of the memory, which we will be discussing shortly in detail. Nixon, other one is catalog. So this is another dynamic memory management function where it is going to allocate space for an area of elements. And it will also initialize all of these elements to zero. And it will return the pointer of the first location. Okay? Then coming to free. This is useful to basically deallocate the memory space which is allocated. Previously. You might have already allocated some memory space using malloc or calloc, but using free, you're going to deallocate the memory that is allocated using malloc calloc, okay, next coming to really lock. So according to real Lock, whenever the dynamically allocated memory space is not sufficient, then you have a chance to relocate. How much you wonder. Okay? So for that purpose, relocation function will be useful, that is realloc function. So it will basically help you to modify the size of whatever allocated space you have done previously. Okay? So these four are the dynamic memory management functions. Okay? So let's discuss in detail about the very first function, which is malloc function. Okay? So as this malloc function is going to allocate the block of memory, it will allocate that whatever our block that you specify, how many blocks you want. Okay, so those many blocks of memory it will allocate. And consider how you are going to allocate this and how the pointer will be pointing to the first location. So the general syntax of the malloc is PTR is equal to the dot type star. You have to specify like this datatype star and then malloc off by its size. So this is the general syntax of using malloc. Okay? Now let us consider an example here. So here I'm going to consider a pointer variable called int star p. Now p is equal to into star. Okay? I'm applying malloc here into star malloc off bite-size. Okay, let us suppose I'm writing like this phi window, size of five into sizeof int. So this is going to basically allocate five into size of inducer, how many bytes it will return the bytes as writer. So size of integer is basically four bytes. Then five into four is equal to 20. So this will allocate 20 bytes of memory space. And this will be pointed by the pointer p. Okay? Point a, b will be pointing to this very first location. So let me show you how this is going to be done. Okay? So first of all, it is creating phi contiguous in memory locations. So phi contiguous in memory locations. So this is 12345, like this. Okay? And consider the very first one is a location called thousand e.g. this will be thousand four. This is thousand eight. Okay? This is 1012 and this is 101.6. So like this, phi contiguous memory locations will be created. And p will be a pointer holding the base address of this particular Adi. So p is a pointer. And this is pointing to the base address just like this. Okay? So now you're going to observe five contiguous memory locations are created. And p is a pointer which is pointing to the base address of the entire array. Okay? So this is done with the help of Melaka. Suppose if memory is not allocated, in that case, p will be pointing to null. Okay? Suppose there is no memory space of phi contiguous memory locations. In that case it has to return null. So generally, okay, if I use a small number, so it will allocate. But let us suppose you are given very large number, okay? And that contiguous memory space, okay? So it doesn't have that much of memory space. In that case, it is going to return null. Okay? So this is about malloc. Now, quickly, we will see about one more function. In order to write any program may require another function which is free function. Okay? So I'll first discuss about free function. Why? Because you have to deallocate to whatever memory that is allocated by you, right? So it is user to de-allocate memory, which is located using pointer de-allocate memory. If you look at the general syntax for free here. So you can write it as free off PDR, writing free off PTR. So it will free the memory allocated by the pointer PTR. Okay? So now let us consider the same example which we have considered already. There is an int star p. P is equal to int star malloc of five into size of int. Now, after this, you want to deallocate whatever memory that is allocated. So you can do this with the help of free writing, free of p. Okay, So this will deallocate the memory which is allocated using pointer p here, okay? And in order to make use of this functions, okay, whichever part of dynamic memory management, you need to include its corresponding header file, which is malloc dot hij share. Okay? So you're going to include malloc dotted share. So let us consider writing a program here. So where you are going to allocate memory with the help of malloc. Okay? So first include the standard header file, which is a stdio.h. Now you want to use this malloc functionality. So for this purpose, include malloc dot hij. This is malloc dotage. Now using main function. Okay? First-time taking a pointer because you need pointer to point to the base address of the memory allocated into star IP, DR. okay. And n is a variable and another variable I'm using AI for basically hydration purpose. And n is representing how many elements you want to store. Okay? So let us allocate memory based on n value using malloc. So first we can prompt the user to basically enter n value or ask the user to enter number of elements. So how many elements are there? You have to enter. So after entering the number of elements, then using scanner if statement, we can read that value into a variable. So that is percentage d address of person-days they are dissolved in. Okay? So using this n value, okay? So we can allocate using malloc where I PDR is pointing to the base address of the memory are located. Here is equal to. Now it has to typecast doing desert pointer because we are trying to store all integer values here, okay? And allocate using malloc, how much of bytes you are allocating. So which is nothing but the yen into size of int, size off in busy. So this will allocate memory for E&M desserts, right? Okay. And after this, using n value, you can start storing elements with the help of scan f statement that okay. So let's see how this can be done. Is, first of all, I'll prompt the user to enter these many elements because you have already taken n value. So you have to play a number of elements. I'm writing enter person days is d elements. Then user starts entering those many limits, okay? And once those elements are entered, okay, then you have to start storing it into the memory allocated using malloc. So this can be done with the help of a loop variable i equal to zero, I less than n i plus, plus. Okay? Using scan f statement you can store, right? So that is a scanner. Percentage should be this is a DR plus I plus I. So the base address is pointed by VTR, okay? When I value is zero, force it will store the element in that location. Then it is incremented by eye. It means it will go to the next location and store the next element. So this is how scanf works here. Now we want to display all the elements which are stored here right now. So you can write a print f statement saying the list of elements. Okay? The list of elements. Okay? Now, using for loop, you can iterate and display all these elements like I equal to zero, I less than n i plus plus. Now start displaying these elements with the help of fprintf statement. Okay? So where do you want content inside the memory location? So use a star because you're trying to access with the help of pointer variable IV TR. So star of ICTR plus I, using which you can access the content inside each of these memory location, which is pointed by IPT. Okay? So once the accessing is done, you just need to deallocate the memory which is already allocated using malloc. For this purpose, you have to use a free off I PTR. We're deallocating memory which is allocated using IP, that is using malloc. Okay? So this is the entire program. Okay? Let's see how this program is going to work for us to fall. In the output screen. Generally. It will ask you to first enter number of elements because program execution starts when the main function, and here it is, printing this statement right there, which is in the number of elements. So let us suppose you have entered a number of elements as fiber. Okay? Then what happens here? It will create phi contiguous memory locations. Okay? So consider here. How this creation happens is using IP TR, okay? I PDR will be the pointer which will be pointing to whatever memory that is allocated using malloc. Okay? Here we are going to say N is equal to five, which means it will create a phi contiguous locations like this. Okay? No. Malloc has to typecast. After that. We are performing typecasting into desert. By default, it will be a wide pointers are generic pointer. So that's where you need to type converted into its corresponding datatype, but as IBD or is an integer pointer. Okay, you have to type converted doing desert. Once the memories are located like this for n value equal to five. Okay? Then if you look at the next statement here, enter percentage d elements, which means it will prompt in the output screen saying that enter five elements because n value is five here. Okay? Now you can start entering those five elements. That is, suppose you have entered 1020304050. These elements are entered. So then these elements will be stored one after the other here, 1020304050. So why? Because since I value is zero, okay? So I PTR plus zero will be representing this location. Okay? So consider this is our dress thousand. This will be thousand, 4,008. This is 1012, this is 1016, okay? Now using IP TRE are pointing to the base address, okay? Now we're going to display the list of elements here. Okay? So finally, it is going to display the list of elimination. The list of elements. What are the elements that you are displaying is using star. You're trying to access each and every element here. So the same elements will be displayed when I equal to zero. This element will be displayed in the next iteration when i equal to one, okay, I PDR will be incremented by one memory location. So this element of 20 will be displayed and so on like this, you are able to display all these elements, okay? And finally, free or five VTR, okay? So which means it is going to basically deallocate the memory which is allocated using ICTR. So you are no longer will be able to access that content. Okay? So this is how the malloc works and also free works. Okay? So this is how you can allocate memory using malloc and deallocate the memory using free. In dynamic memory management. 15. Malloc() Example: So now in this program I'll show you how to basically use this malloc in order to allocate memory dynamically. So first English or D header file, okay? And also include a malloc dot h header file. Okay? In the main function, first, consider the pointer called a star I VTR, okay? And then I is the loop variable. Then n is representing a number of elements that you want to store. Okay? So I'll just prompt the user to basically enter the elements. So number of elements. Okay? And using scanner statement, we can read n value here, either soften. Now using this print f statement, we can prompt like this, enter percentage d elements. Okay? So that is n number of elements you have to enter. Okay? So now using a for-loop, you can read those elements like I equal to zero, I less than n i plus plus. And using statement that, okay. So once you want to basically enter and store, okay. So what is required is you have to allocate memory, isn't it? So once user starts entering the number of elements, so you have to allocate memory, which is using malloc you are allocating here IPR is equal to, okay. So I've gotten wish near. And then using the malloc off, I'm allocating in locations. And each location is often dissident, right? So this is size of InDesign. Okay? So honestly memories are located now. We are going to store here. So that is a IP DR plus i. Okay? So this is how you can store here. And then now we wanted to display this elements which are stored here. So I can just the print f statement saying displaying elements. So in order to display elements, you require, again this for-loop to I trade. Okay? But print f statement to display the content. So percentage d. Okay. To access the content inside it using star, you can access here I PTR plus I. And finally, we will deallocate the memory which is allocated using IP DR. Okay? So let's run this code and see the reserved. You can see it is asking you to enter number of elements. I'm entering value as five. Now. I'm entering 102-030-4050. Okay? So the same elements that are getting displayed here. If you want them to be displayed in some format, okay, Then you can use this person, this 40. So let us enter this time. Only three elements, okay? Those three elements are like 102030. So we can observe here displaying those three elements, 102030. Whatever n value that you are giving. Those many contiguously allocated memory is created. With the help of dynamic memory management function, which is malloc. Pointer will be pointing to the first location. Okay? So was this time I'm entering into number of elements as a ten. So let us suppose those ten elements are like this. Okay? Now you can see here displaying elements 1234 up to ten. All these elements are displayed here. Okay? Now what happens when you are trying to deallocate first and then trying to access the content. Let us overlay I'm replacing the statement I'm removing here and placing here. Okay? Then what happens is you're not able to access that content. You can see because the memories are located. But later you have deallocated the memory, right? So whatever content, some garbage values that are stored in those locations will get printed here. Okay? Because you have allocated memory using malloc here. And later store the content using pointer you have stored. And later immediately you have deallocated memory. Now you're trying to display the content, okay? So in this case, what happens since it is already be allocated? Okay? Now you're trying to display in those locations there will be some garbage values, so they will get printed. Okay? So the tray, you must do this via location of your uses is completed. Okay? Like this. 16. Calloc(): Now we'll discuss evolve. Next function, which is dynamic memory management function called catalog. So generally in this catalog function, it will actually allocate. Just like malloc. It will also allocate memory. But here we are going to allocate mostly these blocks of memory. Malloc. You can say this kind of bytes of memory that you're relocating. But in catalog, you're allocating blocks of memory, like N number of blocks you want delegate, you can allocate it. So it allocates blocks of memory. Okay? Now, let us consider this syntax. So Kellogg, Kellogg syntax can be PTR is equal to data type star. Okay? So you have to write catalog. So generally in malloc you will writing and mean two size of data type. But here it is the N comma size of data type. There will be two arguments for Kellogg function. One is number of blocks followed by size of each block. Okay? So here you have to supply size of datatype. Okay? So this is the general syntax here. Okay? So now once you allocate memory using catalog, so the memory containing different locations, okay? So they will be automatically initialize it to zero, okay? Each of the memory block will be filled with zero. So let me show you here how this is going to work. So consider an example. Like in the star p. So p is the pointer. Now, B is equal to. So using catalog, we're allocating memory here. So the star Galois, cough. Let us suppose I'm writing ten comma sizeof in desert. So here it is going to allocate memory, which is a thin locations of memory, okay? And each location or block is off size of int desert type. And it will fill automatically in each block containing data as zero. Okay? So let us consider here. B is the pointer, okay? Pointing to the base address of the memory, which is a located. So this is first 1, s one, and so on, like this. Okay? Suppose you are considering dislocation as 2000s. And size of integer is four bytes. Okay? So you will see like this and so on. Now, we will be holding the base address of this memory. And each location will be automatically filled with zeros initially, according to catalog. The primary difference between Carlo can malloc is in catalog. We're passing two arguments. Okay? Whereas in case of malloc, we're passing a single argument. In case of scallop, we are allocating blocks of memory. That malloc, we are allocating bytes of memory. So now this is how the entire memory is located and the differences in catalog each of these locations will be initialized to zero. Whereas in case of malloc. There will be garbage values, okay? There'll be garbage values. So let us write a program which makes use of this calloc function in order to create memory dynamically. Okay? So first let us include the header file, which is stdio.h, okay? And also include malloc dot h header file. Okay? Now consider the main function. Okay? So inside this main function, I take your point. A variable that is just like previously we have considered IBD are similarly here also I'm considering a pointer variable star I PTR. Now, we need to prompt the user to enter a number of elements. So here, the number of elements. Okay? So once the user enters a number of elements than using scan f, we can read this number of elements like person-days DI brush often. Okay? Now, using IV TR, we can allocate in locations, okay? So we call it as n blocks of memory can be allocated using calloc all in desert blocks I'm using here. So in Star Catalog off in Goma, sizeof, in desert, in coma sizeof. Okay. Now we need to prompt the user to enter those many elements. Okay? So that is interpersonal tastes, the elements. Okay? So once you enter those many elements, they have to be stored, right? So whatever memory that is allocated using catalog, using which you can store these elements. I equal to zero I less than n I plus plus and using scanner, okay, you can store here, that is a person days of the IBT are less. Okay? So you can store the elements here. Now. You can display the elements just like this. Print f, the list of elements. Okay? So you can write like this, the list of elements. Okay? Now, you can observe here i equal to zero, I less than, I, less Press. Okay. Now let's print these elements using the pointer we can access. Okay? Like start off IPT r plus i, okay? You can access. Finally, you're able to basically read the elements into it and also display the elements. Now we can deallocate the memory which is a located. So again, write free of IP DR, so that whatever memories are located will be deallocated. Okay? So if you look at this program, okay, compare it to the malloc program. This is quite similar, except this particular line is varying, where you have allocated memory using catalog here. And the syntax for the Kellogg. Kellogg off in commas size of datatype. Okay? So this is the only change. Okay? So let us work on it and display the content. Whatever is taken. No, here. Let us read this I-beam pointer, okay? In the end also I. So here we will prompt the user to enter. Number of elements. Number of elements. Okay? So using scan of statement though, we can read it. So percentage should be okay. Now using IP TR, we are going to allocate memory using calloc. So here in Star, Catalog off in karma size often. Okay. So now let us enter those many elements. So we can ask the user to enter those many elements, which is n number of elements. Okay? So once you start entering those many elements using for loop, you can read it. I equal to zero, I less than n I plus plus. Using scanf statement, we can read it percentage d, Okay? I VTR plus i. Okay. Now we can start displaying those elements here. Print f, okay? The list of elements you can display. Okay? So using for loop for I equal to zero, I less than I plus, plus. Okay? Using print f statement, we can display printer, person taste. Be. Okay. Suppose I want some spaces while displaying. You can start off I PTR plus i. Okay. Finally, you can deallocate whatever memory that is allocated using the pointer IBD are. Okay with the help of catalog you have allocated. Okay? So let's run this code and see the result. Enter number of elements. I have entered number of elements as five here. Okay? So the elements are 102-030-4050. Okay? You can see these are displaying those elements exactly. What happens when I remove this free of IP DR. here, and use here. Okay? So let's run this and see the reserve. Five elements and 2030, 40, 50. Okay? Again, you can see here you are de-allocating memory, okay? So after deallocating the memory you're trying to access rate, that is a problem. Okay? So in that case you will get some garbage values. Okay? So that's why you should always use this free of IBD are here after the allocating the memory. That is after accessing all the elements and then start de-allocating memory. One more thing is suppose you're not going to use these lines like entering elements, okay? And storing those elements into this memory. In that case, what will be the reserve? Okay? So let us suppose I have entered values five. And you can see the list of elements are zeros, zeros, zeros 00. Why? Because according to catalog, once the memories are located, okay, it will replace all zeros in those memory locations by default. So that's why you are getting default values as zeros. Okay? So this is how catalog works. 17. Realloc(): So next one is real lock. Okay? So in case of real law, we are going to relocate the memory if the currently allocated memory is insufficient. So the waters a little memory allocation can be done using malloc or calloc. You will start allocating memory later. You want to expand memory, okay? So you can start using real OK. Okay, using the log, you can reallocate memory. General syntax for this. Real lock will be, you can write like this new PDR is equal to data type star. Real lock datatype star, yeah, Lock off all the PDR comma new size or the PDR common size. Okay? So this is real lock corresponding syntax. So what is meant by old PTR here? Okay? So here I can write where old PTR is actually representing the pointer that is pointing to the block of memory which is already allocated using malloc or calloc, as they told horizontally, will be allocating some memory. Using malloc or calloc write. This world pointer is actually representing the pointer pointing to the old memory. To memory. And this memory is allocated using malloc or calloc. Okay? So that is representing this oral memory. Now, what is new sun is? So new size will be representing updated size that you want to allocate using real locker. So I can write here as size of the new block, okay? Or size of the block to be relocated. So again here also, once you relocate memory, new point, there will be no pointing to that newly allocated memory using real OK. so let me show you an example here. So consider an example using real aka first-time considering a pointer in disappointed here in the star b. Now, I'm allocating memory using malloc for this inducer pointer. So this is in the star malloc off. We can write e.g. I. Want to allocate n memory locations. So ten into size off into ten into size of int. Okay? So it will allocate ten locations and each is of size of integer. Now, we can allocate using yellow ocher. So if already allocated memory is not sufficient. Ok? So you're going to locate using real lock. Let us suppose I want 20 locations, new sizes, 20, e.g. so in that case I can write into star real lock off. So what is the world pointer here I'm using the word pointer, a new pointer, both as same P only. So old pointer, common new size. Right now I'm allocating new sizes. 2010 locations or ten blocks are located. Now it is 20 blocks. We are relocating. The world pointer and new pointer both are same, which means the new pointer will be the same point p will be pointing to the newly allocated memory. Okay? So previously here you can see there are ten blocks of memory. Ten into four is equal to 40 bytes of memory is allocated. But using this, this is going to be 2020 into four, which will be 80 bytes of memory will be allocated. For both of these, we are using the same pointer to point. P will be now pointing to the updated memory, which is 80 bytes of memory. Okay? So now let us consider an example here. For real aka. Okay, so first I will basically consider allocating for character pointer. Let me implement directly. Okay? So I'm using a character pointer here. I'm using it character pointer. So where I can write it as cars star name, e.g. okay, star name. So this is my character pointer using the term allocating memory. So that is name is equal to, okay. So star malloc off. Okay. So here let us suppose I'm allocating ten contiguous locations and each is of character datatype, but so which means size of caries, one byte, ten into one is ten bytes of memory I'm allocating using malloc. Okay? So now I want to copy some content into this. You can make use of STR CPI for copying. But for that purpose you have to include another high profile which is a string dot h header file. String dot h header file. Okay? So once I have included, now we're free to use this STR to see BY. Okay. So I'm writing on placing a string called Hyderabad. Okay. So after copying this, now we are trying to print the name which is located at that particular address. Okay, let us suppose I will try to print them. The name which I'm storing, which is a hydro bag, and that is stored at address. Okay. So the iris is percentage p. Okay? So we can write it as a name, comma name. So you can absorb a first-time name will be printed in the exact string format, okay? But second time you can see the same name, but percent SBUs user, which means the address, will be displayed. Okay? Now, this is using malloc we have allocated, let us suppose I want to store a bigger string. Okay? So in that case, this is not sufficient writer, so I'll make use of free lock. Let us suppose star. Okay. So I use realloc and allocate here. Let us suppose some 15 characters and trying to store. So this is a sizeof character type. Okay? So here also semicolon, here also semicolon. Okay? Now I'm trying to copy another string. Okay? Let us suppose name comma. So we just need to take a bigger string then. Okay? So I'll take a string like mini off for this. Okay? So the number of characters are greater than number of characters in Hyderabad. So now let us print similarly here also. Right now the name, corresponding address also am trying to display along with the name. Okay? So once your users is completed, you can just deallocates whatever memory that is allocated here. So free of name, using which you can deallocate memory which is located here. Let us run this code and see reserved. Okay, so I tried to use here, okay. So already we're printing in a different line only. Okay? So right here a slashing and here also slashing. Now you can see name is hydro bot, isn't our dress. Okay. You can observe the corresponding address allocated for this. Now name is minneapolis, and it is normally diapers this particular address. Okay.