C++ Swapping Pointers

Inside your swap function, you are just changing the direction of pointers, i.e., change the objects the pointer points to (here, specifically it is the address of the objects p and q). the objects pointed by the pointer are not changed at all.

You can use std::swap directly. Or code your swap function like the following:

void swap(int *r, int *s)
{
   int temp = *r;
   *r = *s;
   *s = temp;
   return;
}