/* stack3.c , by beck@bofh.ucs.ualberta.ca 
 * This is a dynamically extending integer stack implemented using
 * an array and realloc, instead of using a linked list of
 * integers (a - la stack2.c). This will be much faster
 * than stack2.c in general, because it preserves locality
 * of reference and makes far fewer calls to allocate memory.
 */

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

static int STACK_SIZE = 0;
static int* contents = NULL;
static int top = 0;

void make_empty(void)
{
  top = 0;
}

int is_empty(void)
{
  return top == 0;
}

static int is_full(void)
{
  return top == STACK_SIZE;
}

void push(int i)
{
  if (is_full()) {
    /* remember, STACK_SIZE starts as 0, and the stack contents are NULL. 
     * - read the man page for realloc, when realloc is called with
     * a NULL pointer as it's first argument, it behaves just like malloc().
     * so this one piece of code will both allocate my initial memory, and
     * will make it bigger when I fill up.
     */
    int * tmp;
    STACK_SIZE += 1024;
    tmp = realloc (contents, (STACK_SIZE * sizeof(int)));
	/*C++
	tmp = (int *) realloc (contents, (STACK_SIZE * sizeof(int)));
	*/
    if (tmp == NULL) {
      printf("Error in push: stack is full.\n");
      exit(EXIT_FAILURE);
    }
    else {
      contents = tmp;
    }
  }
  contents[top++] = i;
}

int pop(void)
{
  if (is_empty()) {
    printf("Error in pop: stack is empty.\n");
    exit(EXIT_FAILURE);
  }
  return contents[--top];
}