// fifo.h  -- A queue of integers (dynamic storage)

class Fifo {
	struct node{
		node *next;
		int value;
	};
	node * head;	// whence we dequeue
	node * tail;	// where we enqueue
public:
	Fifo();                // Constructor

	void enqueue(int who); // enqueue a new value

	int dequeue();         // dequeue a value from a fifo

	int isempty();  	// check if a fifo is empty
};


// fifo.cpp  -- A queue of integers (dynamic storage)

#include "fifo.h"

#define NULL 0

// Constructor
Fifo::Fifo()
{
	head = NULL;
	tail = NULL;
}

// enqueue a new value
void Fifo::enqueue(int who)
{
	node *a = new node;

	a->next = NULL;
	a->value = who;
	if (head == NULL)
		head = a;
	else
		tail->next = a;
	tail = a;
}

// dequeue a value from a fifo
int Fifo::dequeue()
{
	node *headNode;
	int who;

	if (head != NULL) {
		headNode = head;
		head = head->next;
		who = headNode->value;
		if (head == NULL)
			tail = NULL;
		delete headNode;
		return who;
	}
	return 0; // You should never execute this
	          // statement (i.e. do not dequeue
			  // from an empty queue)
}

// check if a fifo is empty
int Fifo::isempty()
{
	return (head == NULL);
}


// main.cpp  -- driver for fifo module
//              Read a sequence of positive integers, store them in 
//              a fifo, then print them out


#include <iostream.h>
#include "fifo.h"

void main(void)
{
	int who;
	Fifo queue;

	while(1) {
		cout << "Enter a positive integer [0 to terminate]: ";
		cin >> who;
		if (who <= 0) break;
		queue.enqueue(who);
	};
	while (!queue.isempty()) {
		who = queue.dequeue();
		cout << who << endl;
	}
}