1. POINTERS IN C Pointer Basics, Pointer Arithmetic, Pointer to arrays and Pointer in functions

2. Introduction to Pointer  Variables are stored in the memory  Every variable has unique memory location(Address)  Address can be accessed using ampersand (&) operator

3. Program to display the address of the variable #include void main () { int var1; printf("Address of var1 variable: %x\n", &var1 ); } Address of var1 variable: bff5a400

4. Pointers  A pointer is a variable whose value is the address of another variable  You must declare a pointer before you can use it to store any variable address  Declaring Pointer  Syntax type *var-name;  Eg : int *p1;

5. Program to access the memory location using pointer #include void main () { int var = 20; /* actual variable declaration */ int *ip; /* pointer variable declaration */ ip = &var; /* store address of var in pointer variable*/ printf("Address of var variable: %x\n", &var ); printf("Address stored in ip variable: %x\n", ip ); printf("Value of *ip variable: %d\n", *ip ); } Address of var variable: 64501 Address stored in ip variable: 64501 Value of *ip variable: 20 Address of var variable: 64501 Address stored in ip variable: 64501 Value of *ip variable: 20

6. Program Explanation Memory 20 var1 64501 64502 64503 64504 int var = 20; 20 var 64501 int *ip; ip 65558 ip = &var; 64501 ip 65558

7. Other pointer types int *ip; /* pointer to an integer */ double *dp; /* pointer to a double */ float *fp; /* pointer to a float */ char *ch /* pointer to a character */

8. Null Pointer in C  A pointer that is assigned NULL is called a null pointer.  It is always a good practice to assign a NULL value to a pointer variable in case you do not have exact address to be assigned.  The NULL pointer is a constant with a value of zero

9. Null Pointer – Example Program #include void main () { int *ptr = NULL; printf("The value of ptr is : %x\n", ptr ); } The value of ptr is 0

10. Guess the output of the following program # include void main() { int *p, x=20; p=&x; x= *p+15; printf(“%d”, x); printf(“%d”, *p); }

11. Pointer arithmetic  int *a;  Increment Operator  a++ : address will be incremented by 2 (if it is int)  (*a)++ : content will be incremented by 1  Example  int *a, b=30; /* assume address of b is 2000 */  a=&b;  b++ => 2002  *b++ => 31

12. Pointer arithmetic with Array – Example1 #include void main () { int var[ ] = {10, 100, 200}; int i, *ptr; ptr = &var[0]; printf(“the value is %d\n”, *ptr); ptr++; printf(“the value is %d\n”, *ptr); printf(“the address is %x\n”, ptr); } Assume starting address of var[] is 2500 the value is 10 the value is 100 the address is 2502 the value is 10 the value is 100 the address is 2502

13. Pointer arithmetic with array – Example2 #include void main () { int var[ ] = {10, 100, 200}; int i, *ptr; ptr = &var[0]; printf(“the value is %d\n”, *ptr); (*ptr)++; printf(“the value is %d\n”, *ptr); printf(“the address is %x\n”, ptr); } Assume starting address of var[] is 2500 the value is 10 the value is 11 the address is 2500 the value is 10 the value is 11 the address is 2500

14. Sum of array using pointer – Example 3 #include void main() { int a[5]={1,2,3,4,5}; int i,sum=0; int *b; b=a; for(i=0;i<5;i++) { sum=sum + *b; b++; } printf("\n The Sum is %d",sum); } The Sum is 15

15. Pointer and Functions  Call by value  Call by Reference  Returning pointers

16. Call by value # include int add(int, int); void main() { int no1,no2, sum; printf(“Enter two numbers\t”); scanf(“%d%d”,&no1,&no2); sum=add(no1,no2); printf(“the sum is %d \t”, sum); } int add(int x, int y) { int s; s=x+y; return(s); } Call by Value

17. Call by Reference – Example(swapping of two numbers) # include void swap(int*, int*); void main() { int no1=5, no2=8; printf(“values before swapping %d\t %d\n”, no1,no2); swap(&no1,&no2); printf(“values after swapping %d\t %d”, no1,no2); } void swap(int *x, int *y) { int t; t= *x; *x=*y; *y=t; } Call by Reference values before swapping 58 values after swapping 85 values before swapping 58 values after swapping 85

18. Dynamic memory allocation  Static Memory Allocation  Allocating memory to variable during compile time of your program  Eg. : int a[20];  Disadvantage : Wastage of Memory Space  Dynamic Memory allocation  Allocating memory to variables during run time of your program  Advantage : No wastage of Memory Space

19. Allocating memory during run time # include void main() { int n, *a,k=1; printf(“Enter no. of values “); scanf(“%d”, &n); a= (int *)malloc(n*sizeof(int)); /* malloc(n*2) */ for(i=0;i<n;i++) { *a=k; a++; k++; }