F20 Answer

#include <stdio.h>

void swap( int *x, int *y )
{
  int temp;

  printf("  *x=%d  *y=%d\n", *x, *y ) ;
  temp = *x;
  *x = *y;
  *y = temp;
  printf("  *x=%d  *y=%d\n", *x, *y ) ;
}

void main ( void )
{
  int a = 44, b = 77 ;

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

  system("pause") ;
}

With the proper changes, main and swap coordinate. main passes pointers to its two variables, so now swap can change them. main passes pointers:

swap( &a, &b )

and swap follows these pointers:

temp = *x;

*x = *y;

*y = temp;