stackAndQueueUsingLL.cpp

#include <bits/stdc++.h>
using namespace std;

struct node
{
    int data;
    node *next = NULL;
};

node *FRONT = NULL;
node *REAR = NULL;
node *TOS = NULL;

void MainMenu()
{
    cout << "\n=============Main Menu=============\n";
    cout << "1.Enqueue in Queue \n";
    cout << "2.Dequeue in Queue \n";
    cout << "3.Push in Stack \n";
    cout << "4.Pop in Stack \n";
    cout << "5.Peek in Stack \n";
    cout << "6.Exit \n";
}
void Enqueue(node *&FRONT)
{
    node *ptr = new node();

    int data = 0;
    cout << "Enqueue integer: ";
    cin >> data;
    ptr->data = data;

    if (FRONT == NULL)
    {
        FRONT = ptr;
        REAR = ptr;
        return;
    }

    REAR->next = ptr;
    REAR = ptr;
    return;
}
void Dequeue(node *&FRONT)
{
    if (FRONT == NULL)
    {
        cout << "Queue is empty. Underflow! \n";
        return;
    }
    node *temp = FRONT;
    FRONT = FRONT->next;
    delete (temp);
    return;
}
void traverseQueue(node *FRONT)
{
    node *temp = FRONT;
    while (temp != NULL)
    {
        cout << temp->data << " <- ";
        temp = temp->next;
    }
    cout << "NULL \n";
    return;
}
void Push()
{
    node *ptr = new node();
    int data;
    cout << "Push integer: ";
    cin >> data;
    ptr->data = data;
    if (TOS == NULL)
    {
        TOS = ptr;
        return;
    }
    ptr->next = TOS;
    TOS = ptr;
    return;
}
void pop()
{
    if (TOS == NULL)
    {
        cout << "The Stack is empty. UnderFlow! \n";
        return;
    }
    node *temp = TOS;
    TOS = TOS->next;
    cout << "Popped element is " << temp->data << "\n";
    delete (temp);
}
void peek()
{
    if (TOS == NULL)
    {
        cout << "The Stack is empty. \n";
        return;
    }
    cout << "TOP element is " << TOS->data;
}
void display()
{
    if (TOS == NULL)
    {
        cout << "The Stack is empty. \n";
        return;
    }
    node *temp = TOS;
    // cout << "The stack will be printed in top to down manner instead of bottoms up approach \n";
    while (temp != NULL)
    {
        cout << temp->data <<"\n---------------------\n ";
        temp = temp->next;
    }
    cout << "NULL\n";
    return;
}
int main()
{
    int userChoice = 0;
    node *stackHead = NULL;
    node *queueHead = NULL;

    int numQueueElements;
    cout << "How many elements do you want to initially enqueue in the queue? ";
    cin >> numQueueElements;

    for (int i = 0; i < numQueueElements; i++)
    {
        Enqueue(queueHead);
    }

    int numStackElements;
    cout << "How many elements do you want to initially push into the stack? ";
    cin >> numStackElements;

    for (int i = 0; i < numStackElements; i++)
    {
        Push();
    }

    cout << "Queue after initial enqueues: \n";
    traverseQueue(queueHead);

    cout << "Stack after initial pushes: \n";
    display();

    while (userChoice != 6)
    {
        MainMenu();
        cout << "Enter your choice: ";
        cin >> userChoice;

        switch (userChoice)
        {
        case 1:
            // Enqueue in Queue
            Enqueue(queueHead);
            traverseQueue(queueHead);
            break;
        case 2:
            // Dequeue from Queue
            Dequeue(queueHead);
            traverseQueue(queueHead);
            break;
        case 3:
            // Push to Stack
            Push();
            display();
            break;
        case 4:
            // Pop from Stack
            pop();
            display();
            break;
        case 5:
            // Peek the top element in Stack
            peek();
            break;
        case 6:
            // Exit the loop
            cout << "Exiting...\n";
            userChoice = 6;
            return 0;
        default:
            cout << "Invalid choice, please try again.\n";
        }
    }

    return 0;
}