circular queue implementation.cpp

// Circular Queue implementation in C++

#include <iostream>
#define SIZE 5      /* Size of Circular Queue */

using namespace std;

    class Queue {
   private:
   int items[SIZE], front, rear;

    public:
   Queue() {
    front = -1;
    rear = -1;
  }
  // Check if the queue is full
  bool isFull() {
    if (front == 0 && rear == SIZE - 1) {
      return true;
    }
    if (front == rear + 1) {
      return true;
    }
    return false;
  }
  // Check if the queue is empty
  bool isEmpty() {
    if (front == -1)
      return true;
    else
      return false;
  }
  // Adding an element
  void  enQueue(int element) {
    if (isFull()) {
      cout << "Queue is full";
    }  else {
       if (front == -1) front = 0;
       rear = (rear + 1) % SIZE;
       items[rear] = element;
       cout << endl
          << "Inserted " << element << endl;
     }
      }
  // Removing an element
  int deQueue() {
    int element;
    if (isEmpty()) {
       cout << "Queue is empty" << endl;
       return (-1);
    }  else {
       element = items[front];
        if (front == rear) {
         front = -1;
         rear = -1;
       }
       // Q has only one element,
      // so we reset the queue after deleting it.
       else {
         front = (front + 1) % SIZE;
      }
      return (element);
     }
    }

      void display() {
    // Function to display status of Circular Queue
    int i;
    if (isEmpty()) {
      cout << endl
         << "Empty Queue" << endl;
    } else {
      cout << "Front -> " << front;
      cout << endl
         << "Items -> ";
      for (i = front; i != rear; i = (i + 1) % SIZE)
        cout << items[i];
      cout << items[i];
      cout << endl
     << "Rear -> " << rear;
     }
   }
 };

int main() {
  Queue q;

  // Fails because front = -1
    q.deQueue();
  q.enQueue(1);
  q.enQueue(2);
  q.enQueue(3);
  q.enQueue(4);
  q.enQueue(5);

  // Fails to enqueue because front == 0 && rear == SIZE - 1
  q.enQueue(6);

  q.display();

  int elem = q.deQueue();

  if (elem != -1)
    cout << endl
       << "Deleted Element is " << elem;

  q.display();

  q.enQueue(7);

  q.display();

  // Fails to enqueue because front == rear + 1
  q.enQueue(8);

  return 0;
}