#include <stdio.h>

void swap( int * x, int * y )
{
  int tmp = *x;
  *x = *y;         
  *y = tmp;
}

int main( void )
{
  int a = 5, b = 7;

  swap( &a, &b );     /* must pass the address */
  printf( "%d %d\n", a, b );

  return 0;
}