A Stack Implemented as an array in C

//---------------------------------------------------------------
// File: Code120_Stack.h
// Purpose: Header file for a demonstration of a stack implemented 
//		as an array.  Data type: Character
// Programming Language: C
// Author: Dr. Rick Coleman
//---------------------------------------------------------------
#ifndef CODE120_STACK_H
#define CODE120_STACK_H

#include <stdio.h>

#define MAX_SIZE 50           // Define maximum length of the stack

// List Function Prototypes
void InitStack();             // Initialize the stack
void ClearStack();            // Remove all items from the stack
int Push(char ch);            // Push an item onto the stack
char Pop();                   // Pop an item from the stack
int isEmpty();                // Return true if stack is empty
int isFull();                 // Return true if stack is full

// Define TRUE and FALSE if they have not already been defined
#ifndef FALSE
#define FALSE (0)
#endif
#ifndef TRUE
#define TRUE (!FALSE)
#endif

#endif // End of stack header

//---------------------------------------------------------------
// File: Code120_Stack.c
// Purpose: Implementation file for a demonstration of a stack  
//		implemented as an array.    Data type: Character
// Programming Language: C
// Author: Dr. Rick Coleman
// Date: January 21, 2002
//---------------------------------------------------------------
#include "Code120_Stack.h"

// Declare these as static so no code outside of this source
// can access them.
static int top;	// Declare global index to top of the stack
static char theStack[MAX_SIZE];	// The stack

//--------------------------------------------
// Function: InitStack()
// Purpose: Initialize stack to empty.
// Returns: void
//--------------------------------------------
void InitStack()
{
	top = -1;
}

//--------------------------------------------
// Function: ClearStack()
// Purpose: Remove all items from the stack
// Returns: void
//--------------------------------------------
void ClearStack()
{
	top = -1; // Reset count to start over
}

//--------------------------------------------
// Function: Push()
// Purpose: Push an item onto the stack.
// Returns: TRUE if push was successful
//		or FALSE if the push failed.
//--------------------------------------------
int Push(char ch)
{
	// Check to see if the Stack is full
	if(isFull()) return FALSE;

	// Increment top index
	top++;
	// Add the item to the Stack
	theStack[top] = ch;
	return TRUE;
}

//--------------------------------------------
// Function: Pop()
// Purpose: Pop an item from the Stack.
// Returns: TRUE if pop was successful
//		or FALSE if the pop failed.
//--------------------------------------------
char Pop()
{
	char ch;

	// Check for empty Stack
	if(isEmpty()) return '\0';  // Return null character if stack is empty
	else
	{
		ch = theStack[top];  // Get character to return
		top--;               // Decrement top index
		return ch;           // Return popped character
	}
}

//--------------------------------------------
// Function: isEmpty()
// Purpose: Return true if the stack is empty
// Returns: TRUE if empty, otherwise FALSE
// Note: C has no boolean data type so we use
//	the defined int values for TRUE and FALSE
//	instead.
//--------------------------------------------
int isEmpty()
{
	return (top == -1);
}

//--------------------------------------------
// Function: isFull()
// Purpose: Return true if the stack is full
// Returns: TRUE if full, otherwise FALSE
// Note: C has no boolean data type so we use
//	the defined int values for TRUE and FALSE
//	instead.
//--------------------------------------------
int isFull()
{
	return (top >= MAX_SIZE);
}

//---------------------------------------------------------------
// File: StackMain.c
// Purpose: Main file with tests for a demonstration of a stack  
//		implemented as an array.
// Programming Language: C
// Author: Dr. Rick Coleman
// Date: January 21, 2002
//---------------------------------------------------------------
#include "Code120_Stack.h"

int main(int argc, char **argv)
{
	char	testString[MAX_SIZE + 1];
	int		i;
	char	ch;

	printf("Simple Stack Demonstration\n");
	printf("(Stack implemented as an Array - Stack data type is character.)\n\n");
	printf("Creating a stack\n");

	InitStack();
	printf("Stack created...\n");

	// Test pushing and popping first/last item on a stack
	printf("Testing push and pop of single item.\n");
	Push('A');
	printf("Popped: %c\n", Pop());
	printf("...done\n\n");

	// Test stack by reversing the order of letters in a string
	printf("Enter a string to be reversed (50 characters max)");
	gets(testString); // Assume user is smart enought to not exceed the limit

	// Push all letters on the stack
	i = 0;
	while(testString[i] != '\0')
	{
		Push(testString[i]);
		i++;
	}

	// Pop letters and print in reverse
	printf("Your string printed in reverse is...\n");
	while((ch = Pop()) != '\0') // Pop returns null terminator when stack is empty
		printf("%c", ch);

	printf("\n\n...done.\n");
	return 0;
}