How possible that an memory address also have another memory address ?

Question

I have stored the address of a integer variable in a pointer and then store the address of that previous into another pointer.I am not able to understand how it actually works.

#include <iostream>

using namespace std;

#include <stdio.h>

int main ()
{
    int  var;
    int  *ptr;
    int  **pptr;

    var = 30;

    /* take the address of var */
    ptr = &var;

   /* take the address of ptr using address of operator & */
    pptr = &ptr;

    /* take the value using pptr */
    printf("Value of var = %d\n", var );
    printf("Value available at ptr = %d\n", ptr );
    printf("Value available at pptr = %d\n", pptr);

    return 0;
}

Answer 1

When you do &ptr you get the address of the variable ptr is stored.

So you have a pointer pptr which points at ptr which in turn point at var. Like this:

+------+     +-----+     +-----+
| pptr | --> | ptr | --> | var |
+------+     +-----+     +-----+

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On a side-note, don't use the "%d" format to print pointers. Use "%p" instead, and then cast the pointers to void *.