LinearQueueUsingLinkedLists.cpp

//Queue using linked lists//
#include <iostream>
using namespace std;

struct Node
{
    int data;

    Node *link;
};

Node *front = NULL;
Node *rear = NULL;

bool isempty()
{
    if (front == NULL && rear == NULL)
        return true;
    else
        return false;
}

void enqueue(int value)
{
    Node *ptr = new Node();
    ptr->data = value;
    ptr->link = NULL;

    if (front == NULL)
    {
        front = ptr;
        rear = ptr;
    }
    else
    {
        rear->link = ptr;
        rear = ptr;
    }
}

void dequeue()
{
    if (isempty())
        cout << "Queue is empty\n";
    else if (front == rear)
    {

        front = rear = NULL;
    }
    else
    {
        Node *ptr = front;
        front = front->link;
    }
}

void showfront()
{
    if (isempty())
        cout << "Queue is empty\n";
    else
        cout << "element at front is: " << front->data;
}

void displayQueue()
{
    if (isempty())
        cout << "Queue is empty\n";
    else
    {
        Node *ptr = front;
        while (ptr != NULL)
        {
            cout << ptr->data << " ";
            ptr = ptr->link;
        }
    }
}

int main()
{
    int choice, flag = 1, value;
    while (flag == 1)
    {
        cout << "\n1.enqueue \n2.dequeue \n3.showfront \n4.displayQueue \n5.exit\n";
        cout << "Enter your choice: " << endl;
        cin >> choice;
        switch (choice)
        {
        case 1:
            cout << "Enter Value:\n";
            cin >> value;
            enqueue(value);
            break;
        case 2:
            dequeue();
            break;
        case 3:
            showfront();
            break;
        case 4:
            displayQueue();
            break;
        case 5:
            flag = 0;
            break;
        }
    }

    return 0;
}