// test swap function
//
#include <stdio.h>
#include <math.h>

void badswap( int x, int y) {    int t = x;   x = y;   y = t; }

void goodswap( int *x, int *y) { int t = *x; *x = *y; *y = t; }

int main( void)
{
  int a = 5, b = 10;
  printf( "   before swap: a = %i, b = %i\n", a, b);
  badswap( a, b);
  printf( " after badswap: a = %i, b = %i\n", a, b);
  goodswap( &a, &b);
  printf( "after goodswap: a = %i, b = %i\n", a, b);
  return 0;
}

/* output:

   before swap: a = 5, b = 10
 after badswap: a = 5, b = 10
after goodswap: a = 10, b = 5

*/