A pointer is a variable that contains an address in memory where the value referenced by the pointer is stored. In other words, a pointer is a variable that points to another variable by referring to the other variable’s address. Pointers contain memory addresses, not values. Pointer variables must be declared in C using the * notation. Pointers are widely used to reference data stored in structures and to pass data among functions (by passing the addresses of the data).

For example,

int *ip;  

declares a pointer named ip that points to an integer variable.

Now suppose you want to assign an address to pointer ip. To do this, you can use the & notation. For example,

ip = &a;    

assigns the address of variable a to pointer ip.

You can retrieve the value of variable a that pointer ip is pointing to by

*ip 

Alternatively, you can set the value of the variable that pointer ip points. For example,

*ip = 4;  

assigns a value of 4 to the variable that pointer ip is pointing. The use of pointers is demonstrated by the following:

int a = 1;
int *ip;
ip = &a;    /* &a returns the address of variable a */
printf("content of address pointed to by ip = %d\n", *ip);
*ip = 4;    /* a = 4 */
printf("now a = %d\n", a);

Here, an integer variable a is initialized to 1. Next, ip is declared as a pointer to an integer variable. The address of variable a is then assigned to pointer ip. Next, the integer value of the address pointed to by ip is printed using *ip. (This value is 1.) The value of variable a is then indirectly set to 4 using *ip. The new value of a is then printed. Pointers can also point to the beginning of an array, and are strongly connected to arrays in C.