Queue Program C++

Queue program in C++ using Array and STL

The Queue is one of the most important Linear Data Structure, Queue program follows the FIFO rule i.e First In First Out. The contents in a queue exit in the same order they have entered, if an element is to be removed from the queue then the first element that was added will be removed/deleted.

Operations performed on a Queue

  • Q.push() – insert data into the Queue
  • Q.pop() – remove data from the Queue
  • Q.size() – returns the size of Queue
  • Q.front() – displays the front element of the Queue
  • Q.back() – displays the back element of the Queue

Queue Program using Array in C++

#include <iostream>
using namespace std;
int queue[100], front = -1, rear = -1;

void Insert()
{
    int val;
    if (rear == 100 - 1)
        cout << Queue Overflow << endl;
    else
    {
        if (front == -1)
            front = 0;
        cout << Enter the element to insert in queue :  << endl;
        cin >> val;
        rear++;
        queue[rear] = val;
    }
}
void Delete()
{
    if (front == -1 || front > rear)
    {
        cout << Queue Underflow;
        return;
    }
    else
    {
        cout << Element removed from queue is :  << queue[front] << endl;
        front++;
        ;
    }
}

void Display()
{
    if (front == -1)
        cout << Queue is Empty << endl;
    else
    {
        cout << Elements in queue are : ;
        for (int i = front; i <= rear; i++)
            cout << queue[i] <<  ;
        cout << endl;
    }
}

int main()
{
    int ch;
    cout << 1) Insert to Queue << endl;
    cout << 2) Delete from Queue << endl;
    cout << 3) Display elements of the Queue << endl;
    cout << 4) Exit << endl;
    do
    {
        cout << Enter your choice :  << endl;
        cin >> ch;
        switch (ch)
        {
        case 1:
            Insert();
            break;
        case 2:
            Delete();
            break;
        case 3:
            Display();
            break;
        case 4:
            cout << Exit << endl;
            break;
        default:
            cout << Invalid Choice << endl;
        }
    } while (ch != 4);
    return 0;
}

Output

1) Insert to Queue
2) Delete from Queue
3) Display elements of the Queue
4) Exit
Enter your choice :
1
Enter the element to insert in queue :
1
Enter your choice :
1
Enter the element to insert in queue :
2
Enter your choice :
1
Enter the element to insert in queue :
3
Enter your choice :
2
Element removed from queue is : 1
Enter your choice :
3
Elements in queue are : 2 3
Enter your choice :
4
Exit

Queue Program using STL in C++

#include <iostream>
#include <queue>
using namespace std;
//queue program
void Display(queue<int> q)
{
    queue<int> dq = q;
    while (!dq.empty())
    {
        cout << dq.front() <<" ";
        dq.pop();
    }
    cout << endl;
}

int main()
{
    queue<int> q;
    q.push(1);
    q.push(2);
    q.push(3);

    cout <<" Contents in Queue are : ";
    Display(q);

    cout <<" Front :  "<< q.front() << endl;
    cout <<" Back :  "<< q.back() << endl;
    cout <<" Size :  "<< q.size() << endl;
    cout <<" Popped :  "<< q.front() << endl;
    q.pop();
    Display(q);
    cout <<" FIFO rule First In First Out, 1 was out";
    return 0;
}

Output

Contents in Queue are : 1 2 3
Front : 1
Back : 3
Size : 3
Popped : 1
2 3
FIFO rule First In First Out, 1 was out

This post is part of my #30DaysChallenge to write a blog post every day on what I learn. All the Best ~ Abhiram Reddy

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