//Copyright (c) 1996 A. Michael Berman. All Rights Reserved.
//This code is from "Data Structures via C++: Objects by Evolution", to be
//published by Oxford University Press USA.  Permission is hearby granted to
//use this code for any educational, non-commercial purpose, provided this
//notice remains intact. 
//A. Michael Berman, Rowan College of New Jersey, berman@rowan.edu

// cx9-3.cpp
// Code Example 9-3: Implementation of a Circular Queue

#include "cx9-2.h"

int nextPos(int p) 
{
	if (p == maxQueue - 1) // at end of circle
		return 0;
	else
		return p+1;
}

template < class queueElementType >
Queue < queueElementType >::Queue()
{
	// start both front and rear at 0
	f = 0;
	r = 0;
}

template < class queueElementType >
void
Queue < queueElementType >::enqueue(queueElementType e)
{
	// add e to the rear of the queue, advancing r to next position
	assert(nextPos(r) != f);
	r = nextPos(r);
	elements[r] = e;
}

template < class queueElementType >
queueElementType
Queue < queueElementType >::dequeue()
{
	// advance front of queue, return value of element at the front
	assert(f != r);
	f = nextPos(f);
	return elements[f];
}

template < class queueElementType >
queueElementType
Queue < queueElementType >::front()
{
	// return value of element at the front
	assert(f != r);
	return elements[nextPos(f)];
}

template < class queueElementType >
bool
Queue < queueElementType >::isEmpty()
{
	// return true if the queue is empty, that is,
	// if front is the same as rear
	return f == r;
}