pointer of a pointer in c

Did you know that variables have addresses in memory? Imagine a variable as a home—it contains a value and an address. A pointer is a variable that stores the address of another variable.

To initialize a pointer, we need to specify the type of variable it will point to:

int *p; 

Here, p is declared as a pointer to an integer.

Assigning an Address to a Pointer

We use the address-of operator (&) to assign the address of a variable to a pointer:

int x = 5; p = &x; 

If we print p, it will output a random-looking number—this is the memory address of x. However, if we print p, we get the value stored at that address (which is 5). This operation is called **dereferencing.*

printf("I'm p, the address of x: %p\n", p); // Address of x printf("I'm *p, the value of x: %d\n", *p); // 5 

Note: When printing memory addresses, it's better to use %p instead of %d.

Modifying a Variable Through a Pointer

*p = 20; printf("%d", x); // 20 

This means that changing *p also changes x.

Pointer to a Pointer (Double Pointer)

Even a pointer has its own memory address, and we can store that address in another pointer! To initialize a pointer that holds the address of another pointer, we write:

int **q; q = &p; 

The first * indicates that q is a pointer.
The second * means that q stores the address of another pointer.

Accessing Values Using a Double Pointer

Since q holds the address of p,

• *q is the value inside p, which is the address of x.

• **q is the value of x.
  More simply:

• q → Address of p.

• *q → Value inside p (which is &x).

• **q → Value inside x (which is 5).
  Final Code
  

#include <stdio.h> int main() { int *p; int x = 5; p = &x; int **q; q = &p; printf("I'm q, the address of p: %p\n", q); printf("I'm the address of p: %p\n", &p); printf("I'm the value of p (the address of x): %p\n", *q); printf("I'm the address of x: %p\n", &x); printf("I'm the value of x: %d\n", x); printf("I'm the value of the variable with address p (so I'm x): %d\n", **q); return 0; }