#include <iostream>

class Queue{
  int front;
  int rear;
  int size;
  int *arr;
public:
  // declare the member functions
  Queue(const int size);
  ~Queue();
  void enqueue(const int elem);
  void dequeue();
  void display();
};

// function definitions

// creates a queue with the given size
Queue::Queue(const int size){
  Queue::size = size;
  front = -1;
  rear = -1;
  arr = new int[size];
}

Queue::~Queue(){
  delete [] arr;
}

// adds an element to the queue
void Queue::enqueue(const int elem){
  // if the queue is full then return beacuse we have an overflow
  if(front == 0 and rear == size - 1){
    std::cout << "QUEUE OVERFLOW!\n";
    return;
  }

  // else add the element to the queue
  if(front < 0) front++;
  rear++;
  arr[rear] = elem;
}

void Queue::dequeue(){
  // if the queue is empty then return because we have an underflow
  if(front == -1 and rear == -1){
    std::cout << "QUEUE UNDERFLOW!\n";
    return;
  }
  // else decrement rear by one
  rear--;
  // if rear is less than front then there are no elements present and we set both to -1
  if(rear < front){
    rear = -1;
    front = -1;
  }
}

void Queue::display(){
  // if queue is empty then return because there is nothing to display
  if(front == -1 && rear == -1){
    return;
  }

  // else print from the front to rear
  for(int i = front; i <= rear; i++){
    std::cout << arr[i] << " ";
  }
  std::cout << "\n";
}

int main(int argc, char const *argv[]) {
  Queue queue(5);
  queue.enqueue(10);
  queue.enqueue(20);
  queue.enqueue(30);
  queue.enqueue(40);
  queue.enqueue(50);
  queue.display();
  queue.dequeue();
  queue.display();
  return 0;
}