﻿ C++ Find the position of an element in a queue

# C++ Queue Exercises: Find the position of an element in a queue

## C++ Queue: Exercise-24 with Solution

Write a C++ program to find the position of an element in a queue.

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
}

int find_position(Queue q, int x) {
int pos = 0;
Queue temp;

// Traverse the queue and search for the element
while (!q.isEmpty()) {
pos++;
int curr = q.peek();
q.dequeue();
temp.enqueue(curr);
if (curr == x) {
// Element found, restore the queue and return the position
while (!temp.isEmpty()) {
q.enqueue(temp.peek());
temp.dequeue();
}
return pos;
}
}

while (!temp.isEmpty()) {
q.enqueue(temp.peek());
temp.dequeue();
}
cout << "Error: Element " << x << " not found in queue." << endl;
return -1;
}

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;
}

};

int main() {
cout << "Initialize a Queue." << endl;
Queue q1; // Creating an instance of Queue
cout << "\nInsert some elements into the queue:" << endl;
q1.enqueue(0);
q1.enqueue(1);
q1.enqueue(2);
q1.enqueue(3);
q1.enqueue(4);
q1.enqueue(5);
q1.enqueue(6);
q1.display(); // Display elements of the queue
int x = 2;
cout << "\nPosition of the element x = " << x << " is " << q1.find_position(q1, x) << endl;
x = 3;
cout << "\nPosition of the element x = " << x << " is " << q1.find_position(q1, x) << endl;
x = 6;
cout << "\nPosition of the element x = " << x << " is " << q1.find_position(q1, x) << endl;
return 0;
}
```
```

Sample Output:

```Initialize a Queue.

Insert some elements into the queue:
Queue elements are: 0 1 2 3 4 5 6

Position of the element x = 2 is 3

Position of the element x = 3 is 4

Position of the element x = 6 is 7
```

Flowchart:

CPP Code Editor: