/*********************************************************
 * From C PROGRAMMING: A MODERN APPROACH, by K. N. King  *
 * Copyright (c) 1996 W. W. Norton & Company, Inc.       *
 * All rights reserved.                                  *
 * This program may be freely distributed for class use, *
 * provided that this copyright notice is retained.      *
 *********************************************************/

/* stack2.c (Chapter 19, page 425) */

#include <stdio.h>
#include <stdlib.h>
#include "stack.h"

struct node {
  int data;
  struct node* next;
};

static struct node* top = NULL;

void make_empty(void)
{
  top = NULL;
}

int is_empty(void)
{
  return top == NULL;
}

void push(int i)
{
  struct node* new_node;

  new_node = malloc(sizeof(struct node));
    /*C++
    new_node = (struct node *) malloc(sizeof(struct node));
    */
  if (new_node == NULL) {
    printf("Error in push: stack is full.\n");
    exit(EXIT_FAILURE);
  }

  new_node->data = i;
  new_node->next = top;
  top = new_node;
}

int pop(void)
{
  struct node* old_top;
  int i;

  if (is_empty()) {
    printf("Error in pop: stack is empty.\n");
    exit(EXIT_FAILURE);
  }

  old_top = top;
  i = top->data;
  top = top->next;
  free(old_top);
  return i;
}