// A stack class is defined here with a private internal storage
// and public functions that can manipulate it.

// include this file in any program that needs a stack of characters
// This stack is based on ../c/stack.[ch] and uses a linked list.
// Upgraded to 1997 style C++ in Feb 1998

#include <stdlib.h>
#include <iostream.h>
struct top_t{
	char d;
	top_t *next;
};
struct stack{
private:
	top_t * tp;
public:
	void make_new() { tp=0; }
	char top() { if(tp)return (tp -> d);else cerr<<"\ntop: empty stack"; exit(1); }
	bool empty()	{ return !tp; }
	void push(char c)
	{	top_t * temp;
		temp = new top_t;
		temp->d = c;
		temp->next = tp;
		tp = temp;
	}
	char pop() 
	{ 	top_t * t1 = tp; char x;
		if(! empty() ){
			x = t1->d;
			tp = t1->next;
			delete t1;
			return x;
		}
		else
			cerr<<"\npop: empty stack\n";
	}
	bool full() { return false; }//Note: For compatability

	stack(){make_new();}  //auto initialization
	~stack(){while(!empty())pop();}  // automatic destruction
};