﻿ C++ Remove all even elements from a queue

# C++ Queue Exercises: Remove all even elements from a queue

## C++ Queue: Exercise-15 with Solution

Write a C++ program to remove all even elements from a queue.

Sample Solution:

C Code:

``````#include <iostream>
#include <map>
#include <cmath>

using namespace std;

const int MAX_SIZE = 100;

class Queue {
private:
int front; // Holds the front index of the queue
int rear; // Holds the rear index of the queue
int arr[MAX_SIZE]; // Array to hold 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); // Checks if the queue is full
}

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

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

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

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

void remove_even(Queue & q) {
Queue temp; // Temporary queue to hold non-even elements
while (!q.isEmpty()) {
int x = q.peek();
q.dequeue();
if (x % 2 != 0) {
temp.enqueue(x); // Enqueue non-even elements to temp queue
}
}
while (!temp.isEmpty()) {
q.enqueue(temp.peek()); // Enqueue back non-even elements to the original queue
temp.dequeue();
}
}
};

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.enqueue(6);
q.display();
cout << "\nRemove all even numbers from the said queue:" << endl;
q.remove_even(q);
q.display();
return 0;
}
```
```

Sample Output:

```Initialize a Queue.

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

Remove all even numbers from the said queue:
Queue elements are: 1 3 5
```

Flowchart:

CPP Code Editor: