///////////////////////////stack3.C///////////////
#include <assert.h>
#include <iostream.h>

enum boolean {BAD, GOOD};

class Istack {
	class node {  //linked list stack
	public:
		int data;
		node* next;
	};
	node* new_node(int , node* );
	node* top;
public:
	// Note that Nitems is not used
	void init( int Nitems=100 ) { top = NULL; }
	void push(int x) {top = new_node(x, top); }
	int pop();
	boolean isempty() { return ((top == NULL) ?BAD :GOOD); }
	boolean isfull() { return (BAD); }
};


// Linked list implementation of stacks.

Istack :: node* Istack :: new_node(int d, node* n)
{
	node* t = new node;
	assert( t );		// space found OK
	t -> data = d;
	t -> next = n;
	return( t );		// return pointer to stack
}

int Istack :: pop()
{
	assert( isempty() == GOOD);
	int t = top -> data;
	node* oldtop = top;
	top = top -> next;
	delete oldtop;		// removes node that held
	return t;			// data item being returned
}

void main()
{
	Istack s1, s2;
	int i;

	s1.init(500);
	s2.init();
	
	for( i = 0; i < 20; i++ ) {
		s1.push(i);
	}

	for( i = 0; i < 20; i++ ) {
		cout << s1.pop() << ' ';
	}
	cout << endl;
	
	s2.push(10);
	i = s2.pop();
}