Question

#include <stdio.h>

int main()
{
    int *p = (int*) 60;    --- Line 1
    int *q = (int*) 40;    --- Line 2
    printf("%d", p-q);    //Output is 5
    return 0;
}

Could anybody please explain to me the output of this program?

Answer 1

It means the (implementation-defined) action of assigning an integral value to a pointer happens. This often means that p points to the memory address at 60 and q to the address at 40. These memory addresses could be in virtual memory, hardware memory, and many implementations have different conversion routines for these.

Since this is implementation-defined anything could happen, as described by your implementation.

But isn’t this entirely worthless?

It’s most certainly not, it is used a lot in embedded hardware programming to access certain features or call built-in functions.

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Most likely on your system int is 4 bytes wide, so p - q equals (60 - 40) / 4 == 5.