#import "Stack.h"

@implementation Stack

#define NULL_LINK (StackLink *) 0

+ new
{
  self = [super new];
  top = (StackLink *) 0;
  return self;
}

- free
{
  StackLink *next;

  while (top != NULL_LINK)
    {
      next = top->next;
      free ((char *) top);
      top = next;
    }
  return [super free];
}

- push: (int) value
{
  StackLink *newLink;

  newLink = (StackLink *) malloc (sizeof (StackLink));
  if (newLink == 0)
    {
      fprintf(stderr, "Out of memory\n");
      return nil;
    }
  newLink->data = value;
  newLink->next = top;
  top = newLink;
  size++;

  return self;
}

- (int) pop
{
  int value;
  StackLink *topLink;

  if (0 != size)
    {
      topLink = top;
      top = top->next;
      value = topLink->data;
      free (topLink);
      size--;
    }
  else
    {
      value = 0;
    }
  return value;
}

- (unsigned int) size
{
  return size;
}

@end