15IT102 Program Design and Development. John Blesswin (101922) Department of Computer Science and Engineering SRM University

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1 15IT102 Program Design and Development John Blesswin (101922) Department of Computer Science and Engineering SRM University

2 Book to follow Programming in ANSI C 5th Edition by E. Balagurusamy Let us C 8th Edition by Y. P. Kanetkar 2

3 UNIT 5 Pointers Pointers and Indirection, Defining a Pointer Variable, Pointers in Expressions - Operations Pointers : Arithmetic Operations, Relational Operations - Array of Pointers : character strings - Passing Pointers to functions - Pointers to structures 3

4 Pointers Pointers are powerful features of C and (C++) programming that differentiates it from other popular programming languages like: Java and Python. Pointers are used in C program to access the memory and manipulate the address #include <stdio.h> int main(){ int var=5; printf("value: %d\n",var); printf("address: %u",&var); //Notice, the ampersand(&) before var. Value: 5 Address:

5 Defining pointer variables In C, there is a special variable that stores just the address of another variable. It is called Pointer variable or, simply, a pointer. data_type* pointer_variable_name; int* p; 5

6 Example 1 #include <stdio.h> int main(){ int* pc; int c; c=22; printf("address of c:%u\n",&c); printf("value of c:%d\n\n",c); pc=&c; printf("address of pointer pc:%u\n",pc); printf("content of pointer pc:%d\n\n",*pc); c=11; printf("address of pointer pc:%u\n",pc); printf("content of pointer pc:%d\n\n",*pc); *pc=2; printf("address of c:%u\n",&c); printf("value of c:%d\n\n",c); Address of c: Value of c: 22 Address of pointer pc: Content of pointer pc: 22 Address of pointer pc: Content of pointer pc: 11 Address of c: Value of c: 2 6

7 Null Pointers It is always a good practice to assign a NULL value to a pointer variable in case you do not have an exact address to be assigned. This is done at the time of variable declaration. A pointer that is assigned NULL is called a null pointer. #include <stdio.h> int main () { int *ptr = NULL; printf("the value of ptr is : %x\n", ptr ); The value of ptr is 0 7

8 Pointer expression We can use pointer variables in expression. int x = 10, y = 20, z; int *ptr1 = &x; int *ptr2 = &y; z = *ptr1 * *ptr2 ; Will assign 200 to variable z. 8

9 Pointer Increment and Scale Factor We can use increment operator to increment the address of the pointer variable so that it points to next memory location. int *ptr; ptr++; It will increment the address of pointer variable by 2. So if the address of pointer variable is 2000 then after increment it becomes

10 Pointer Arithmetic A pointer in c is an address, which is a numeric value. Therefore, you can perform arithmetic operations on a pointer just as you can on a numeric value. There are four arithmetic operators that can be used on pointers: ++, --, +, and - 10

11 Incrementing a Pointer Example 1 #include <stdio.h> const int MAX = 3; int main () { int var[] = {10, 100, 200; int i, *ptr; Address of var[0] = bf882b30 Value of var[0] = 10 Address of var[1] = bf882b34 Value of var[1] = 100 Address of var[2] = bf882b38 Value of var[2] = 200 /* let us have array address in pointer */ ptr = var; for ( i = 0; i < MAX; i++) { printf("address of var[%d] = %x\n", i, ptr ); printf("value of var[%d] = %d\n", i, *ptr ); /* move to the next location */ ptr++; 11

12 Pointer Relational Operations #include <stdio.h> const int MAX = 3; int main () { int var[] = {10, 100, 200; int i, *ptr; Address of var[0] = bfdbcb20 Value of var[0] = 10 Address of var[1] = bfdbcb24 Value of var[1] = 100 Address of var[2] = bfdbcb28 Value of var[2] = 200 ptr = var; i = 0; while ( ptr <= &var[max - 1] ) { printf("address of var[%d] = %x\n", i, ptr ); printf("value of var[%d] = %d\n", i, *ptr ); /* point to the previous location */ ptr++; i++; 12

13 Arrays of Pointer Example 1 #include <stdio.h> int main() { int i, classes[6],sum = 0; printf("enter 6 numbers:\n"); for(i = 0; i < 6; ++i) { // (classes + i) is equivalent to &classes[i] scanf("%d",(classes + i)); Enter 6 numbers: Sum = 21 // *(classes + i) is equivalent to classes[i] sum += *(classes + i); printf("sum = %d", sum); 13

14 Arrays of Pointer Example 2 #include <stdio.h> const int MAX = 3; Value of var[0] = 10 Value of var[1] = 100 Value of var[2] = 200 int main () { int var[] = {10, 100, 200; int i, *ptr[max]; for ( i = 0; i < MAX; i++) { ptr[i] = &var[i]; /* assign the address of integer. */ for ( i = 0; i < MAX; i++) { printf("value of var[%d] = %d\n", i, *ptr[i] ); 14

15 Character Strings A pointer which pointing to an array which content is string, is known as pointer to array of strings. 15

16 Printing Address of the Character Array #include<stdio.h> int main() { int i; Address of String 1 = 178 Address of String 2 = 180 Address of String 3 = 184 Address of String 4 = 189 char *arr[4] = {"C","C++","Java","VBA"; char *(*ptr)[4] = &arr; for(i=0;i<4;i++) printf("address of String %d : %u\n",i+1,(*ptr)[i]); 16

17 Printing Contents of character array #include<stdio.h> int main() { int i; String 1 = C String 2 = C++ String 3 = Java String 4 = VBA char *arr[4] = {"C","C++","Java","VBA"; char *(*ptr)[4] = &arr; for(i=0;i<4;i++) printf("string %d : %s\n",i+1,(*ptr)[i]); 17

18 Passing Pointers to functions #include <stdio.h> /* function declaration */ double getaverage(int *arr, int size); int main () { /* an int array with 5 elements */ int balance[5] = {1000, 2, 3, 17, 50; double avg; /* pass pointer to the array as an argument */ avg = getaverage( balance, 5 ) ; /* output the returned value */ printf("average value is: %f\n", avg ); double getaverage(int *arr, int size) { int i, sum = 0; double avg; for (i = 0; i < size; ++i) { sum += *arr[i]; avg = (double)sum / size; return avg; Average value is:

19 Pointers to structures #include <stdio.h> #include <string.h> struct student { int id; char name[30]; float percentage; ; Records of STUDENT1: Id is: 1 Name is: Raju Percentage is: int main() { int i; struct student record1 = {1, "Raju", 90.5; struct student *ptr; ptr = &record1; printf("records of STUDENT1: \n"); printf(" Id is: %d \n", ptr->id); printf(" Name is: %s \n", ptr->name); printf(" Percentage is: %f \n\n", ptr->percentage); 19

20 Summary For more details refer srmnotes.weebly.com