C program to display relation between pointer to pointer

In C programming language, pointer to pointer or double pointer is a variable that holds the address of another pointer.

Declaration

Given below is the declaration for pointer to pointer −

datatype ** pointer_name;

For example, int **p;

Here, p is a pointer to pointer.

Initialization

‘&’ is used for initialization.

For example,

int a = 10;
int *p;
int **q;
p = &a;

Accessing

Indirection operator (*) is used for accessing

Sample program

Following is the C program for double pointer −

#include<stdio.h>
main ( ){
   int a = 10;
   int *p;
   int **q;
   p = &a;
   q = &p;
   printf("a =%d ",a);
   printf(" a value through pointer = %d", *p);
   printf(" a value through pointer to pointer = %d", **q);
}

Output

When the above program is executed, it produces the following result −

a=10
a value through pointer = 10
a value through pointer to pointer = 10

Example

Now, consider another C program which shows the relationship between pointer to pointer.

#include<stdio.h>
void main(){
   //Declaring variables and pointers//
   int a=10;
   int *p;
   p=&a;
   int **q;
   q=&p;
   //Printing required O/p//
   printf("Value of a is %d\n",a);//10//
   printf("Address location of a is %d\n",p);//address of a//
   printf("Value of p which is address location of a is %d\n",*p);//10//
   printf("Address location of p is %d\n",q);//address of p//
   printf("Value at address location q(which is address location of p) is %d\n",*q);//address of a//
   printf("Value at address location p(which is address location of a) is %d\n",**q);//10//
}

Output

When the above program is executed, it produces the following result −

Value of a is 10
Address location of a is 6422036
Value of p which is address location of a is 10
Address location of p is 6422024
Value at address location q(which is address location of p) is 6422036
Value at address location p(which is address location of a) is 10