﻿ C++ Implement a queue using an array

# C++ Queue Exercises: Implement a queue using an array

## C++ Queue: Exercise-1 with Solution

Write a C++ program to implement a queue using an array with enqueue and dequeue operations. Find the top element of the stack and check if the stack is empty, full or not.

Note: Putting items in the queue is called enqueue, and removing items from the queue is called dequeue.

Sample Solution:

C Code:

``````#include <iostream>

using namespace std;

const int MAX_SIZE = 100;

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

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; // If the queue is empty, update front to 0
rear = 0; // If the queue is empty, update rear to 0
} else {
rear++; // Increment rear index
}
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; // If the queue has only one element, update front to -1
rear = -1; // If the queue has only one element, update rear to -1
} else {
front++; // Increment front index
}
}

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;
}
};

int main() {
cout << "Initialize a Queue." << endl;
Queue q;
cout << "\nIs the Queue is empty? " << q.isEmpty() << endl;
cout << "\nInsert some elements into the queue:" << endl;
q.enqueue(1);
q.enqueue(2);
q.enqueue(3);
q.enqueue(4);
q.enqueue(5);
cout << "\nIs the Queue full? " << q.isFull() << endl;
cout << "\nIs the Queue is empty? " << q.isEmpty() << endl;
q.display();
cout << "\nFront element is " << q.peek() << endl;
cout << "\nRemove two elements from the Queue" << endl;
q.dequeue();
q.dequeue();
q.display();
cout << "\nFront element is " << q.peek() << endl;
return 0;
}
```
```

Sample Output:

```Initialize a Queue.

Is the Queue is empty? 1

Insert some elements into the queue:

Is the Queue full? 0

Is the Queue is empty? 0
Queue elements are: 1 2 3 4 5

Front element is 1

Remove two elements from the Queue
Queue elements are: 3 4 5

Front element is 3
```

Flowchart:

CPP Code Editor: