# C++ Queue Exercises: Find the second lowest element of a queue

## C++ Queue: Exercise-12 with Solution

Write a C++ program to find the second lowest element of a queue.

Sample Solution:

C Code:

``````#include <iostream>

#include <map>
#include <cmath>

using namespace std;

const int MAX_SIZE = 100;

// Class representing a Queue data structure
class Queue {
private:
int front;
int rear;
int arr[MAX_SIZE];

public:
// Constructor initializing the Queue
Queue() {
front = -1;
rear = -1;
}

// Check if the Queue is full
bool isFull() {
return (rear == MAX_SIZE - 1);
}

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

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

// Remove an element from the Queue (dequeue)
void dequeue() {
if (isEmpty()) {
cout << "Error: Queue is empty" << endl;
return;
}
if (front == rear) {
front = -1;
rear = -1;
} else {
front++;
}
}

// Get the front element of the Queue
int peek() {
if (isEmpty()) {
cout << "Error: Queue is empty" << endl;
return -1;
}
return arr[front];
}

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

// Function to find the second lowest element in the Queue
int second_lowest(Queue q) {
int min1 = INT_MAX;
int min2 = INT_MAX;
while (!q.isEmpty()) {
int val = q.peek();
q.dequeue();
if (val < min1) {
min2 = min1;
min1 = val;
} else if (val < min2) {
min2 = val;
}
}
return min2;
}
};

// Main function
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();

int sh_el = q.second_lowest(q);
cout << "Second lowest element of the said queue: " << sh_el << endl;

cout << "\nInsert two more elements into the queue:" << endl;
q.enqueue(0);
q.enqueue(7);
q.display();

sh_el = q.second_lowest(q);
cout << "Second lowest element of the said queue: " << sh_el << endl;

return 0;
}

```
```

Sample Output:

```Initialize a Queue.

Insert some elements into the queue:
Queue elements are: 1 2 3 4 5
Second lowest element of the said queue: 2

Insert two more elements into the queue:
Queue elements are: 1 2 3 4 5 0 7
Second lowest element of the said queue: 1
```

Flowchart:

CPP Code Editor: