/*-------------------------------------------------------------------*/
/* stackarrayao.c (A Stack Abstract Object Implementation as an Array)*/
/*-------------------------------------------------------------------*/

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

#define INITIAL_PHYS_LENGTH 2

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

/* The state of the Stack */

static double *pdArray;
static int iTop;
static int iPhysLength;
static int iInitialized = 0;

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

void Stack_init(void)

/* Initialize the Stack.
   It is a checked runtime error for the Stack to be initialized. */

{ 
   assert(! iInitialized);  
   pdArray = (double*)calloc(INITIAL_PHYS_LENGTH, sizeof(double));
   assert(pdArray != NULL);  
   iTop = 0;
   iPhysLength = INITIAL_PHYS_LENGTH;
   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);
   free(pdArray);
   iInitialized = 0;
}

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

static void Stack_grow(void)

/* Double the physical length of the Stack. */

{
   assert(iInitialized);
   iPhysLength *= 2;
   pdArray = (double*)realloc(pdArray, sizeof(double) * iPhysLength);
   assert(pdArray != NULL);
}

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

void Stack_push(double dItem)

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

{
   assert(iInitialized);
   
   if (iTop == iPhysLength)
      Stack_grow();

   pdArray[iTop] = dItem;
   iTop++;
}

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

double Stack_pop(void)

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

{
   assert(iInitialized);
   assert(iTop > 0);
   iTop--;
   return pdArray[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;
}