/*------------------------------------------------------------------*/
/* stackao.c:  A Stack Abstract Object                              */
/*------------------------------------------------------------------*/

#include <assert.h>
#include <stdlib.h>
#include "stackao.h"

#define MAX_STACK_SIZE 100

/*------------------------------------------------------------------*/

/* The state of the Stack */

static int iInitialized = 0;
static int piContents[MAX_STACK_SIZE];
static int iTop;

/*------------------------------------------------------------------*/

void Stack_init(void)

/* Initialize the Stack. 
   It is a checked runtime error for the Stack to be initialized. */
 
{
   assert(! iInitialized);
   iTop = 0;
   iInitialized = 1;
}

/*------------------------------------------------------------------*/

void Stack_free(void)

/* Free the resources consumed by the Stack.
   It is a checked runtime error for the Stack to be uninitialized. */

{
   assert(iInitialized);
   iInitialized = 0;
}

/*------------------------------------------------------------------*/

void Stack_push(int iItem) 

/* Push iItem onto the Stack. 
   It is a checked runtime error for the Stack to uninitialized or to
   be full. */

{
   assert(iInitialized);
   assert(! Stack_isFull());

   piContents[iTop] = iItem;
   iTop++;
}

/*------------------------------------------------------------------*/

int Stack_pop(void) 

/* Pop the Stack, and return the popped item.
   It is a checked runtime error for the Stack to be uninitialized
   or to be empty. */ 

{
   assert(iInitialized);
   assert(! Stack_isEmpty());

   iTop--;
   return piContents[iTop];
}

/*------------------------------------------------------------------*/
 
int Stack_isEmpty(void) 

/* Return 1 (TRUE) iff the Stack is empty.
   It is a checked runtime error for the Stack to be uninitialized. */ 

{
   assert(iInitialized);
   return iTop == 0; 
}

/*------------------------------------------------------------------*/
 
int Stack_isFull(void) 

/* Return 1 (TRUE) iff the Stack is full.
   It is a checked runtime error for the Stack to be uninitialized. */ 

{
   assert(iInitialized);
   return iTop == MAX_STACK_SIZE; 
}