#ifndef FALSE
#define FALSE 0
#endif
#ifndef NULL
#define NULL 0
#endif

//   This is Vstack.h
template<class T>
    class Gstack {
    public:
    	virtual void push(T) = 0; 	// pure virtual function
    	virtual T pop() = 0; 		// pure virtual function
    	virtual bool isempty() = 0;	// pure virtual function
    	virtual bool isfull() = 0; 	// pure virtual function
    };

//    This is Arraystack.h
#include <assert.h>
template<class T>
    class Array_stack : public Gstack<T> {
    	int sz;
    	int top;
    	T* astack;
    public:
    	Array_stack(int Nitems = 100)
    		{ sz = Nitems; astack = new T[sz]; top = sz; }
    	~Array_stack() 
		    { delete[] astack; }
    	void push(T x) 
		    { assert( !isfull() ); astack[--top] = x; }
    	T pop() 
		    { assert( !isempty() ); return( astack[top++] ); }
    	bool isempty() 
		    { return( top == sz ); }
    	bool isfull() 
		    { return( top == 0 ); }
    };

//    This is Linkedstack.h
template<class T>
    class Link_stack : public Gstack<T> {
    	struct node {
    		T data;
    		node* next;
    		node(T d, node* n) 
			    { data = d; next = n; }
    	};
    	node* top;
    public:
    	Link_stack( int Nitems = 100 ) 
		    { top = NULL; }
    	void push(T x) 
		    { top = new node(x, top); }
    	T pop() {
        	assert( !isempty() );
        	T t = top -> data;
        	node* oldtop = top;
        	top = top -> next;
        	delete oldtop;
        	return t;
    	}

    	bool isempty() 
		    { return( top == NULL ); }
    	bool isfull() 
		    { return( FALSE ); }
    };

//    This is reverse.cc
#include <iostream.h>
//#include "Vstack.h"
// Doesn't know about Arraystack or Linkedstack
void reverse( Gstack<int> &, int );	// a prototype

void reverse( Gstack<int> &s, int n )
{
        int i;

        for( i = 0; i < n; i++ ) {
                s.push('a'+i);
        }
        for( i = 0; i < n; i++ ) {
                cout << s.pop() << ' ';
        }
        cout << endl;
}
//    This is main.cc
//#include "Vstack.h"
//#include "Linkedstack.h"
//#include "Arraystack.h"
//extern void reverse( stack<int> &s, int n );

int main()
{
	Array_stack<int> s1(500);
	Link_stack<int> s2;	// or s2(137); but not s2();
	Array_stack<char> s3;
	Link_stack<char> s4(50);

	reverse (s1, 20);
	reverse (s2, 20);
//	reverse (s3, 20);	//problem reverse only knows about integers
//	reverse (s4, 20);	//need to make reverse a member function, perhaps?
	return 0;
}
/*  
////////////Code Warrior warns ///////////
Warning : variable 'Nitems' is not used in function
Stack.cc line 94   void main()

Warning : variable 'Nitems' is not used in function
Stack.cc line 94   void main()

116 115 114 113 112 111 110 109 108 107 106 105 104 103 102 101 100 99 98 97 
116 115 114 113 112 111 110 109 108 107 106 105 104 103 102 101 100 99 98 97
*/
/*
////////////////g++ says: //////////////
Stack.cc:95: warning: return type for `main' changed to integer type
Stack.cc:38: warning: `class Array_stack<int>' has virtual functions but
	non-virtual destructor
Stack.cc:38: warning: `class Array_stack<char>' has virtual functions
	but non-virtual destructor
Stack.cc: In function `int main(...)':
Stack.cc:99: warning: unused variable `class Link_stack<char> s4'
Stack.cc: In method `Link_stack<int>::Link_stack(int)':
Stack.cc:52: warning: unused parameter `int Nitems'
Stack.cc: In method `Link_stack<char>::Link_stack(int)':
Stack.cc:52: warning: unused parameter `int Nitems'
116 115 114 113 112 111 110 109 108 107 106 105 104 103 102 101 100 99 98 97
116 115 114 113 112 111 110 109 108 107 106 105 104 103 102 101 100 99 98 97
*/