#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void swap ( int *a, int *b )
{
  int tmp = *a;
  *a = *b;
  *b = tmp;
}

int main ( void )
{
  int a = 10, b = 20;

  swap ( &a, &b );
  printf ( "a: %d\nb: %d\n", a, b );

  return 0;
}

a: 20
b: 10