queue.cpp

// Implement Queue data structure in C++
/*
    In this implementation, the Queue class has private member variables front, rear, and arr to keep track of the front and rear 
    indices of the queue and the elements in the queue, respectively. The class also has public member functions isFull(), isEmpty(), 
    enqueue(), dequeue(), peek(), and print() for checking if the queue is full or empty, adding elements to the rear of the queue, 
    removing elements from the front of the queue, peeking at the element at the front of the queue, and printing the elements in the 
    queue, respectively. The main() function demonstrates how to use the Queue class by creating a new queue object q, adding three 
    elements to the queue, removing one element from the front of the queue, peeking at the element at the front of the queue, and 
    printing the elements in the queue
*/
#include <iostream>
using namespace std;

const int MAX_SIZE = 100; // maximum size of the queue

class Queue {
private:
    int front, rear;
    int arr[MAX_SIZE];
public:
    Queue() {
        front = -1; // initialize front and rear to -1 to indicate the queue is empty
        rear = -1;
    }

    bool isFull() {
        return rear == MAX_SIZE - 1; // check if the rear index is at the maximum size
    }

    bool isEmpty() {
        return front == -1 && rear == -1; // check if both front and rear indices are at -1, indicating an empty queue
    }

    void enqueue(int x) {
        if (isFull()) {
            cout << "Error: Queue is full" << endl;
            return;
        }
        if (isEmpty()) {
            front = rear = 0; // if the queue is empty, set both front and rear to 0 to add the first element
        }
        else {
            rear++; // increment rear to add the new element
        }
        arr[rear] = x; // add the new element to the rear of the queue
    }

    void dequeue() {
        if (isEmpty()) {
            cout << "Error: Queue is empty" << endl;
            return;
        }
        if (front == rear) {
            front = rear = -1; // if the queue has only one element, set both front and rear indices to -1 to indicate an empty queue
        }
        else {
            front++; // increment front to remove the element
        }
    }

    int peek() {
        if (isEmpty()) {
            cout << "Error: Queue is empty" << endl;
            return -1;
        }
        return arr[front]; // return the element at the front of the queue
    }

    void print() {
        if (isEmpty()) {
            cout << "Queue is empty" << endl;
            return;
        }
        cout << "Queue: ";
        for (int i = front; i <= rear; i++) {
            cout << arr[i] << " "; // print each element in the queue from front to rear
        }
        cout << endl;
    }
};

int main() {
    Queue q;
    q.enqueue(1);
    q.enqueue(2);
    q.enqueue(3);
    q.print(); // output: Queue: 1 2 3
    q.dequeue();
    q.print(); // output: Queue: 2 3
    cout << "Front element: " << q.peek() << endl; // output: Front element: 2
    return 0;
}