Queue - DSA | Part 6 |

A queue is a useful data structure in programming. It is similar to the ticket queue outside a cinema hall, where the first person entering the queue is the first person who gets the ticket.

Queue follows the First In First Out (FIFO) rule - the item that goes in first is the item that comes out first.

In programming terms, putting items in the queue is called enqueue, and removing items from the queue is called dequeue.

Basic Operations of Queue

A queue is an object (an abstract data structure - ADT) that allows the following operations:

• Enqueue: Add an element to the end of the queue
• Dequeue: Remove an element from the front of the queue
• IsEmpty: Check if the queue is empty
• IsFull: Check if the queue is full
• Peek: Get the value of the front of the queue without removing it

---

Queue Implementations in C++

#include <iostream>
#define SIZE 5

using namespace std;

class Queue {
   private:
  int items[SIZE], front, rear;

   public:
  Queue() {
    front = -1;
    rear = -1;
  }

  bool isFull() {
    if (front == 0 && rear == SIZE - 1) {
      return true;
    }
    return false;
  }

  bool isEmpty() {
    if (front == -1)
      return true;
    else
      return false;
  }

  void enQueue(int element) {
    if (isFull()) {
      cout << "Queue is full";
    } else {
      if (front == -1) front = 0;
      rear++;
      items[rear] = element;
      cout << endl
         << "Inserted " << element << endl;
    }
  }

  int deQueue() {
    int element;
    if (isEmpty()) {
      cout << "Queue is empty" << endl;
      return (-1);
    } else {
      element = items[front];
      if (front >= rear) {
        front = -1;
        rear = -1;
      } 
      else {
        front++;
      }
      cout << endl
         << "Deleted -> " << element << endl;
      return (element);
    }
  }

  void display() {
    int i;
    if (isEmpty()) {
      cout << endl
         << "Empty Queue" << endl;
    } else {
      cout << endl
         << "Front index-> " << front;
      cout << endl
         << "Items -> ";
      for (i = front; i <= rear; i++)
        cout << items[i] << "  ";
      cout << endl
         << "Rear index-> " << rear << endl;
    }
  }
};

int main() {
  Queue q;


  q.deQueue();


  q.enQueue(1);
  q.enQueue(2);
  q.enQueue(3);
  q.enQueue(4);
  q.enQueue(5);


  q.enQueue(6);

  q.display();


  q.deQueue();


  q.display();

  return 0;
}

Comments

[Kostas Kalafatis]

Great job on the implementation! In the future, you might want to consider breaking down each operation into separate code snippets, and including a brief paragraph that describes the method. This will help readers understand the logic behind each step more clearly and make it easier for them to follow your code.

[Madhuban Khatri]

thank you bro for your suggestion.