#include <stdio.h>

void swap(int *p, int *q){
  int   tmp;

  tmp = *p;
  *p = *q;
  *q = tmp;
}


int main(void){
  int   a = 3, b = 7;           /* We want to exchange the values of a and b */

  printf("%d  %d\n", a, b);     /* 3  7 is printed */
  swap(&a, &b);
  printf("%d  %d\n", a, b);     /* 7  3 is printed */
  return 0;
}