#include <stdio.h>

void swap(int a, int b) {
  int t = a;

  a = b;
  b = t;

  printf("swap: a = %d, b = %d\n",a,b);
}

int main(void) {
  int a = 21;
  int b = 17;

  printf("main: a = %d, b = %d\n",a,b);
  
  swap(a, b);

  return 0;
}