/* 
Sandra N. Kardaras-Flick 
03/27/05

STACKS

A program that inputs a line of text and uses a stack to print the line reversed.

*/

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

#define STACK_SIZE 50
#define TRUE 1
#define FALSE 0

/* defines a new type, boolean, as a synonym for int */
typedef int boolean;

/* function declarations */
void makeEmptyStack(void);   /* function to make the stack empty */
boolean stackIsEmpty(void);  /* function returns true if stack is empty */
boolean stackIsFull(void);   /* function returns true if stack is full */

void push(int i);            /* push the integer i onto the stack */
int pop(void);               /* pop off the top integer from the stack */

void stackOverflow(void);  /* error when you try to remove from empty stack */
void stackUnderflow(void); /* error whey you try to add to a full stack */

/* array of integers that stores the stack */
int contentsOfStack[STACK_SIZE];

/* pointer to the top of the stack */
int *top_ptr = &contentsOfStack[0];

int main()
{
	int temp = 0;       /* int to store each input */
	
	makeEmptyStack();   /* set the stack empty */
	
	printf("\n\n\n\n\t   Enter your text:\t");
	
	/* loop getting characters until end of line is reached */
	while ((temp = getchar()) != '\n')
	{
	
	/* push the character in temp onto the stack */
	push(temp);
	}
	printf("\tYour text reversed:\t");
	
	while (!stackIsEmpty())  /* when stack is empty the loop will exit */
	{
	
	/* pop an int off the stack and display  */
	printf("%c", pop());
	}
	
	printf("\n\n\n\n");
	return 0;
	}
	
/* make the stack empty. */
void makeEmptyStack(void)
{
	top_ptr = &contentsOfStack[0];
}

/* check if the stack is empty.*/
boolean stackIsEmpty(void)
{
	return top_ptr == &contentsOfStack[0];
}

/* check if the stack is full. */
boolean stackIsFull(void)
{
	return top_ptr == &contentsOfStack[STACK_SIZE];
}

/* add int i to the end of the array. */
void push(int i)
{
	if (stackIsFull())       /* can't add more to a full stack */
	stackOverflow();     	 /* print overflow message and exit */
	else
		*top_ptr++ = i;       /* add i to the array, then increase top_ptr */
}

/* take the top int off the stack and return it. */
int pop(void)
{
	if (!stackIsEmpty())		/* can't pop from an empty stack */
	return *--top_ptr;    	/* return the int at *top_ptr, and decrment top_ptr */
	else
		stackUnderflow();		/* print error message and exit */
		return 0;
}

/* print stack overflow error message and exit the program */
void stackOverflow(void)
{
	printf("\nStack Overflow\n");
	exit(EXIT_FAILURE);
}

/* print stack underflow  error message and exit the program */
void stackUnderflow(void)
{
	printf("\nStack Underflow\n");
	exit(EXIT_FAILURE);
}