In C language, a pointer to a pointer is a type of pointer that holds the memory address of another pointer. It's represented by a double indirection operator (**). A pointer to a pointer is useful in situations where you need to pass a pointer to a function, but you also want the function to be able to modify the pointer itself.

Here's an example of a pointer to a pointer:

Copy code

#include <stdio.h> int main() {    int x = 10;    int* p = &x;    int** pp = &p;  // pp is a pointer to a pointer    printf("%d\n", **pp);  // prints 10    return 0; }

In this example, the variable x is an integer, p is a pointer that holds the memory address of x, and pp is a pointer to a pointer that holds the memory address of p. To access the value of x, we dereference pp twice, first as a pointer and then as an integer.

Here's an example of a function that takes a pointer to a pointer as an argument and modifies the pointer:

Copy code

#include <stdio.h> void func(int** pp) {    int y = 20;    *pp = &y; } int main() {    int x = 10;    int* p = &x;    func(&p);    printf("%d\n", *p);  // prints 20    return 0; }

In this example, the func function takes a pointer to a pointer pp as an argument. Inside the function, it creates a new integer y with the value 20, and assigns the address of y to the pointer pp points to, thus changing the value of p and the value it points to.

It's worth noting that, when working with pointer to pointer, you need to be