#include <iostream.h>
#include <stdlib.h>
 
const int STACK_SIZE = 6;
const int NIL = -1;
const int LAST_ELEMENT = STACK_SIZE - 1;
 
struct  stackType
{
	int tos;
	char data[STACK_SIZE];
};
 
 
 
void create(stackType&);
bool full(stackType);
bool empty(stackType);
void Push(char, stackType& );
void Pop(char&,stackType& );
void Top( char&, stackType);
 
void display(stackType);
 
void create(stackType& s)
{
	s.tos = NIL;
}
 
bool full(stackType s)
{
	if(s.tos == LAST_ELEMENT)
		return true;
	else
		return false;
}
 
bool empty(stackType s)
{
	if (s.tos == NIL)
		return true;
	else
		return false;
}
 
void Push(stackType& s, char achar)
{
	s.tos = s.tos + 1;
	s.data[s.tos] = achar;
}
 
void Pop(stackType& s, char& achar)
 
{
	achar = s.data[s.tos];
	s.tos = s.tos + 1;
}
 
void display(stackType s)
{
	int i;
	for (i = s.tos; i != NIL; i++)
		cout << s.data[i] << endl;
}
 
void Top(stackType s, char& achar)
{
	achar = s.data[s.tos];
}
 
void main()
{
	stackType aStack[3];
 
	char command, letter;
	int use_stack = 0;
	system("cls");
 
	for (int i = 0 ; i<3 ; i++) create(aStack[i]);
 
	cout << "This program uses a stack implemented as an array\n";
	cout << "Maximum number of items = " << STACK_SIZE << endl;
 
	do
	{
		cout << "\nMAKING USE OF STACK " << use_stack;
		cout << "\n[P]ush data, P[O]p data, [T]op show top data";
		cout << "\n[D]isplay stack, [S]witch stack or [Q]uit -> ";
		cin >> command;
		switch(command)
		{
			case 'p' :
			case 'P' :	if(!full(aStack[use_stack]))
							{
								cout << "Enter data -> ";
								cin >> letter;
								Push(aStack[use_stack],letter);
							}
							else
								cout << "The stack is full data not pushed\n";
								break;
			case 'o' :
			case 'O' :	if (!empty(aStack[use_stack]))
							{
								Pop(aStack[use_stack], letter);
								cout << letter << " has been popped\n";
							}
							else
								cout << "Stack empty cannot pop\n";
							break;
			case 't' :
			case 'T' :	if (!empty(aStack[use_stack]))
							{
								Top(aStack[use_stack], letter);
								cout << letter << " is on top of the stack\n";
								cout << "\n";
							}
							else
								cout  << "Stack empty cannot pop\n";
							break;
			case 's' :
			case 'S' :	do
							{
								cout << "Which stack do you wish to use (0-2) ";
								cin >> use_stack;
							} while (use_stack < 0 || use_stack > 2);
							break;
			case 'd' :
			case 'D' :	if (!empty(aStack[use_stack]))
								display(aStack[use_stack]);
							else
								cout << "stack empty no data to display\n";
								break;
			case 'q' :
			case 'Q' :	cout << "Program terminated\n";
							break;
			default  :	cout << "Unknown command [" <<command << "] try again!\n";
							break;
			}
	 }	while (!(command == 'q' || command == 'Q'));
}