Listing 4: ptr_net.c

/*
  ptr_net.c

  A test program illustrating structures and pointers.

  B.McMullin, February 1993.

*/

#include <stdio.h>

struct bucket_s
{
  struct bucket_s *black, *white;
  int quantity;
};

struct bucket_s n0, n1, n2, n3;

void red_connections(void)
{
  n0.black = &n1;
  n0.white = &n3;
  n3.black = n0.black;
  n3.white = &n0;
  n1.white = NULL;
  n1.black = &n2;
  n2.white = n3.black;
  n2.black = n1.white;
}

void blue_connections(void)
{
  n0.white = &n1;
  n1.black = &n0;
  n0.black = n0.white->black;
  n1.white = n1.black->white;

  n2.black = &n3;
  n3.black = &n2;
  n2.white = n2.black->black;
  n3.white = n3.black->white;
}

void yellow_connections(void)
{
  struct bucket_s *p;

  p = n0.white;
  n0.white = n1.white;
  n1.white = n2.white;
  n2.white = n3.white;
  n3.white = p;

  p = n0.black;
  n0.black = n1.black;
  n1.black = n2.black;
  n2.black = n3.black;
  n3.black = p;

}

void massage(void)
{
   n0.black->quantity = 2 * n3.white->quantity;
   n1.black->quantity = 2 * n2.white->quantity;
   n0.white->quantity = 2 * n2.quantity;
}

void main(void)
{
  n0.quantity = 2;
  n1.quantity = -3;
  n2.quantity = 4;
  n3.quantity = -5;

  red_connections();
  massage();
  blue_connections();
  yellow_connections();
  massage();

/*
  printf("n0.quantity: %d\n", n0.quantity);
  printf("n1.quantity: %d\n", n1.quantity);
  printf("n2.quantity: %d\n", n2.quantity);
  printf("n3.quantity: %d\n", n3.quantity);
*/
}