﻿ C++ Reverse the elements of a queue

# C++ Queue Exercises: Reverse the elements of a queue

## C++ Queue: Exercise-2 with Solution

Write a C++ program to reverse the elements of a queue.

Sample Solution:

C Code:

``````#include <iostream>
#include <stack> // Include the stack library for using stacks

using namespace std;

const int MAX_SIZE = 100;

class Queue {
private:
int front;
int rear;
int arr[MAX_SIZE];

public:
Queue() {
front = -1; // Initialize front index to -1
rear = -1; // Initialize 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 message if queue is full
return;
}
if (isEmpty()) {
front = 0;
rear = 0;
} else {
rear++;
}
arr[rear] = x; // Insert the element at the rear index
}

void dequeue() {
if (isEmpty()) {
cout << "Error: Queue is empty" << endl; // Display error message if 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 message if 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 message if 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 reverse the elements of the queue
void reverseQueue(Queue & q) {
if (q.isEmpty()) {
cout << "Error: Queue is empty" << endl; // Display error message if queue is empty
return;
}
stack < int > s; // Create a stack to store elements temporarily
while (!q.isEmpty()) {
s.push(q.peek()); // Push each element of the queue to the stack
q.dequeue(); // Remove the element from the queue
}
while (!s.empty()) {
q.enqueue(s.top()); // Enqueue the elements from the stack to the queue
s.pop(); // Pop the element from the stack
}
}
};

int main() {
cout << "Initialize a Queue." << endl;
Queue q;
cout << "\nInsert some elements into the queue:" << endl;
q.enqueue(1);
q.enqueue(2);
q.enqueue(3);
q.enqueue(4);
q.enqueue(5);
q.display();
q.reverseQueue(q); // Reverse the elements of the queue
cout << "\nReverse Queue elements:\n";
q.display();
return 0;
}
```
```

Sample Output:

```Initialize a Queue.

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

Reverse Queue elements:
Queue elements are: 5 4 3 2 1
```

Flowchart:

CPP Code Editor: