Pointers are used in C program

Pointers are used in C program to access the memory and manipulate the address.

Pointer variable or simply pointer are the special types of variables that holds memory address rather than data, that is, a variable that holds address value is called a pointer variable or simply a pointer.

Dynamic memory allocation, cannot be performed without using pointers.

If  x is a variable then, &x is the address in memory.

Reference operator(&)

/* Example to demonstrate use of reference operator in C programming. */

#include <stdio.h>
int main()

{
int var=5;
printf("Value: %d\n",var);
printf("Address: %d",&var);
return 0;
}

Output

Value: 5
Address: 2898058

Reference operator(*)

/* Source code to demonstrate, handling of pointers in C program */

#include <stdio.h>
int main()

{
int  * pc;   // declaration of pointer
int c;
c=22;
printf("Address of c:  %d  \n",&c);
printf("Value of c:  %d  \n\n", c);
pc=&c;
printf("Address of pointer pc:%d\n",pc);
printf("Content of pointer pc:%d\n\n",*pc);
c=11;
printf("Address of pointer pc:%d\n",pc);
printf("Content of pointer pc:%d\n\n",*pc);
*pc=2;
printf("Address of c:%d\n",&c);
printf("Value of c:%d\n\n",c);
return 0;

}

Output
Address of c: 2686784
Value of c: 22

Address of pointer pc: 2686784
Content of pointer pc: 22

Address of pointer pc: 2686784
Content of pointer pc: 11

Address of c: 2686784
Value of c: 2

Commonly done mistakes in pointers

Suppose, the programmer wants  pointer pc to point to the address of c. Then,

int c, *pc;
pc=c;             /* pc is address whereas, c is not an address. */
*pc=&c;           /* &c is address whereas, *pc is not an address. */

In both cases, pointer pc is not pointing to the address of c.

#include <stdio.h>
int main()
{
int first, second, *p, *q, sum;
printf("Enter two integers to add\n");
scanf("%d%d", &first, &second);
p = &first;
q = &second;
sum = *p + *q;
printf("Sum of entered numbers = %d\n",sum);
return 0;
}

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int c, *pc ; 
// c is variable & pc is pointer. c can hold value & pc can hold memory address.

c=25;
pc=&c ;