What is pointer to pointer in C?

In case of a pointer to pointer concept, one pointer refers to the address of another pointer. The pointer to pointer is a chain of pointers. Generally, the pointer contains the address of a variable. The pointer to pointer contains the address of a first pointer. Let's understand this concept through an example:

#include <stdio.h>  
 int main()  
{  
    int a=10;  
    int *ptr,**pptr; // *ptr is a pointer and **pptr is a double pointer.  
    ptr=&a;  
    pptr=&ptr;  
    printf("value of a is:%d",a);  
    printf("\n");  
    printf("value of *ptr is : %d",*ptr);  
    printf("\n");  
    printf("value of **pptr is : %d",**pptr);  
    return 0;  
}  

In the above example, pptr is a double pointer pointing to the address of the ptr variable and ptr points to the address of 'a' variable.