﻿ C++ Copy one queue to another

# C++ Queue Exercises: Copy one queue to another

## C++ Queue: Exercise-20 with Solution

Write a C++ program to copy one queue to another.

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 copy elements from q1 to q2
void copy_Queue(Queue& q1, Queue& q2) {
if (q1.isEmpty()) {
cout << "Error: Queue is empty" << endl; // Display error if q1 is empty
return;
}
for (int i = q1.front; i <= q1.rear; i++) {
q2.enqueue(q1.arr[i]); // Copy elements from q1 to q2
}
}
};

int main() {
cout << "Initialize a Queue." << endl;
Queue q1, q2, q3; // Creating instances of 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
cout << "Is q2 is blank? " << q2.isEmpty() << endl; // Check if q2 is empty
cout << "Is q3 is blank? " << q3.isEmpty() << endl; // Check if q3 is empty
cout << "\nCopy the elements of q1 to q2:" << endl;
q1.copy_Queue(q1, q2); // Copy elements from q1 to q2
cout << "Queue-2" << endl;
q2.display(); // Display elements of queue 2
cout << "\nCopy the elements of q3 to q1:" << endl;
q1.copy_Queue(q3, q1); // Copy elements from q3 to q1
return 0;
}

Sample Output:

Initialize a Queue.

Insert some elements into the queue:
Queue-1
Queue elements are: 1 2 3 4
Is q2 is blank? 1
Is q3 is blank? 1

Copy the elements of q1 to q2:
Queue-2
Queue elements are: 1 2 3 4

Copy the elements of q3 to q1:
Error: Queue is empty

Flowchart:

CPP Code Editor: