Queue.cpp

/**
Program for creating the queue using the linked list.
Program performs all the operations such as push, pop and display.
It takes care of queue underflow condition.
**/

#include <iostream>
#include <cstdlib>

using namespace std;


// Declaration for data structure of linked queue
template <class T>
class Lqueue {
	private:
	typedef struct queue {
		T data;
		struct queue *next;
	}node;

	node *front, *rear;

	public:
	Lqueue() {
		front = NULL;
		rear = NULL;
	}
	
	void enqueue();
	void display();
	void dequeue();	
};

/*enqueue function*/
template <class T>
void Lqueue <T> ::enqueue() {
	node *temp = new node;
	temp->next = NULL;
	cout << "Enter the new item:" << endl;
	cin >> temp->data;
	if (front == NULL)
		front = temp;
	else
		rear->next = temp;
	rear = temp;
}
/*dequeue function*/
template <class T>
void Lqueue <T>::dequeue() {
	if (front == NULL)
		cout << "No more elements left. Stack underflow." << endl;
	else {
		node *temp = new node;
		cout << "The dequeued item is: " << front->data << endl;
		temp = front;
		front = front->next;
		delete temp;
	}
}
/*Display function*/
template <class T>
void Lqueue <T>::display() {
	if(front == NULL)
		cout << "The queue is empty.";
	else{
		node *temp = new node;
		temp = front;
		cout << "Queue display:" << endl;
		while (temp != NULL) {
			cout << " " << temp->data;
			temp = temp->next;
		}
	}
	cout << endl;
}
/*main*/
void main() {
	int choice;
	char ans = 'y';
	Lqueue <int> queue; // object for int type
	cout << "queue using Linked List" << endl;
	while(ans == 'y') {
		cout << "Main menu" << endl;
		cout << "1. Enqueue\n2. Dequeue\n3. Display" << endl;
		cout << "Enter your choice:" << endl;
		cin >> choice;
		switch(choice) {
			case 1: queue.enqueue(); break;
			case 2: queue.dequeue(); break;
			case 3: queue.display(); break;
			default: exit(0);
		}
		cout << "Do you want to continue? y/n" << endl;
		cin >> ans;
	}
}