C++ Queue Exercises: Concatenate two queues

C++ Queue: Exercise-19 with Solution

Write a C++ program to concatenate two queues.

Sample Solution:

C Code:

#include <iostream> // Including necessary library for input and output operations

using namespace std;

const int MAX_SIZE = 100; // Maximum size for the queue

class Queue {
private:
    int front; // Front of the queue
    int rear; // Rear of the queue
    int arr[MAX_SIZE]; // Array to store queue elements

public:
    Queue() {
        front = -1; // Initializing front index to -1
        rear = -1; // Initializing rear index to -1
    }

    bool isFull() {
        return (rear == MAX_SIZE - 1); // Check if the queue is full
    }

    bool isEmpty() {
        return (front == -1 && rear == -1); // Check if the queue is empty
    }

    void enqueue(int x) {
        if (isFull()) {
            cout << "Error: Queue is full" << endl; // Display error if the queue is full
            return;
        }
        if (isEmpty()) {
            front = 0;
            rear = 0;
        }
        else {
            rear++;
        }
        arr[rear] = x; // Add an element to the rear of the queue
    }

    void dequeue() {
        if (isEmpty()) {
            cout << "Error: Queue is empty" << endl; // Display error if the queue is empty
            return;
        }
        if (front == rear) {
            front = -1;
            rear = -1;
        }
        else {
            front++;
        }
    }

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

    void display() {
        if (isEmpty()) {
            cout << "Error: Queue is empty" << endl; // Display error if the queue is empty
            return;
        }
        cout << "Queue elements are: ";
        for (int i = front; i <= rear; i++) {
            cout << arr[i] << " "; // Display all elements in the queue
        }
        cout << endl;
    }

    // Function to concatenate two queues
    void concatenate(Queue& q1, Queue& q2) {
        while (!q2.isEmpty()) {
            q1.enqueue(q2.peek()); // Enqueue elements from q2 into q1
            q2.dequeue(); // Dequeue elements from q2
        }
    }
};

int main() {
    cout << "Initialize a Queue." << endl;
    Queue q1, q2, result_queue;
    cout << "\nInsert some elements into the queue:" << endl;
    q1.enqueue(1);
    q1.enqueue(2);
    q1.enqueue(3);
    q1.enqueue(4);
    cout << "Queue-1" << endl;
    q1.display(); // Display elements of queue 1
    q2.enqueue(5);
    q2.enqueue(6);
    q2.enqueue(1);
    cout << "Queue-2" << endl;
    q2.display(); // Display elements of queue 2
    q1.concatenate(q1, q2); // Concatenate queue 1 and queue 2
    cout << "\nConcatenate said two queues:" << endl;
    q1.display(); // Display concatenated queue
    return 0;
}

Sample Output:

Initialize a Queue.

Insert some elements into the queue:
Queue-1
Queue elements are: 1 2 3 4 
Queue-2
Queue elements are: 5 6 1 

Concatenate said two queues:
Queue elements are: 1 2 3 4 5 6 1 

Flowchart:

CPP Code Editor:

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Previous C++ Exercise: Remove all elements greater than a number from a queue.
Next C++ Exercise: Copy one queue to another.