Implementing a Circular Queue in C++

A circular queue is a linear data structure that follows the First In First Out (FIFO) principle but unlike a traditional queue, the last position is connected back to the first position to make a circle. It is very useful for managing resources in computing environments where the system needs to run continuously.

Program Code

#include <iostream>
using namespace std;

class CircularQueue {
private:
    int front, rear, size;
    int *queue;

public:
    CircularQueue(int size) {
        this->size = size;
        queue = new int[size];
        front = rear = -1;
    }

    ~CircularQueue() {
        delete[] queue;
    }

    // Function to insert an element at the rear of the queue
    void enqueue(int value) {
        if ((front == 0 && rear == size - 1) || (rear == (front - 1) % (size - 1))) {
            cout << "Queue is Full\n";
        } else if (front == -1) { // Insert First Element
            front = rear = 0;
            queue[rear] = value;
        } else if (rear == size - 1 && front != 0) {
            rear = 0;
            queue[rear] = value;
        } else {
            rear++;
            queue[rear] = value;
        }
    }

    // Function to delete an element from the front of the queue
    void dequeue() {
        if (front == -1) {
            cout << "Queue is Empty\n";
        } else if (front == rear) {
            cout << "Element " << queue[front] << " is removed\n";
            front = rear = -1;
        } else if (front == size - 1) {
            cout << "Element " << queue[front] << " is removed\n";
            front = 0;
        } else {
            cout << "Element " << queue[front] << " is removed\n";
            front++;
        }
    }

    // Function to display the elements of the queue
    void displayQueue() {
        if (front == -1) {
            cout << "Queue is Empty\n";
            return;
        }
        cout << "Elements in the Circular Queue are: ";
        if (rear >= front) {
            for (int i = front; i <= rear; i++)
                cout << queue[i] << " ";
        } else {
            for (int i = front; i < size; i++)
                cout << queue[i] << " ";
            for (int i = 0; i <= rear; i++)
                cout << queue[i] << " ";
        }
        cout << endl;
    }
};

int main() {
    CircularQueue q(5);

    // Enqueue elements
    q.enqueue(14);
    q.enqueue(22);
    q.enqueue(13);
    q.enqueue(-6);
    q.enqueue(25);

    q.displayQueue();

    q.dequeue();
    q.displayQueue();

    q.enqueue(23);
    q.displayQueue();

    return 0;
}

Class and Function Documentation

• Constructor CircularQueue(int size): Initializes the queue of given maximum size.
• void enqueue(int value): Adds a value to the rear of the queue. If the queue is full, it will output “Queue is Full”.
• void dequeue(): Removes the front item of the queue and prints it. If the queue is empty, it will output “Queue is Empty”.
• void displayQueue(): Prints all elements in the queue from front to rear. This method demonstrates the circular nature of the queue if it wraps around.

Example Usage

    CircularQueue q(5);
    q.enqueue(14);
    q.enqueue(22);
    q.enqueue(13);
    q.dequeue();
    q.displayQueue();  // Output will show remaining elements in the queue