Circular_Queue.cpp

/*
This is a code of circular queue data structure. It is a linear data structure, which obeys the principal
 of First in First Out(FIFO). Circular queue data structure is a updated version of linear queue data structure,
 which have some advantages over linear queue. The following code shows the implementation of circular queue data structure,
 in a very clean and understandable way.
*/

#include<iostream>
#include<stdlib.h>

// Defining max size of the queue as 5

#define max 5

using namespace std;

// Writing a class where all the basic functions of the circular queue presides

class CircularQueue
{
    /*
    Defining all the variables as public variables.
    (It is not necessory of define the variables as public,you can define the variables as private also)*/       
    public:
    int front;
    int rear;
    int arr[max];

    // Initializing a default constructor of the class
    CircularQueue(){
    front = -1;
    rear = -1;
        for(int i = 0; i < max; i++){
            arr[i] = 0;
        }
    }

    // Defining the isFull function to check whether the queue is full or not
    bool isFull(){
        if ((rear + 1) % max == front)
            return true;
        else
            return false;
    }

    // Defining the isEmpty function to check whether the queue is empty or not
    bool isEmpty(){
        if (front == -1 && rear == -1)
            return true;
        else
            return false;
    }

    // Defining the enqueue function, to insert an item in the queue
    void enqueue(int item){
        if(isFull())
        {
            cout << "Queue is full" << endl;
        }
        else if (isEmpty()){
            front=rear=0;
            arr[rear] = item;
        }
        else {
            rear = (rear + 1) % 5;
            arr[rear] = item;
        }

    }

    // Defining the dequeue function, to delete item from the queue
    int dequeue(){
        int x = 0;       
        if(front == rear){
          x = arr[front];
          front = rear = -1;
          return x;
        }
        else
        {
            x = arr[front];
            arr[front] = 0;
            front = (front + 1) % 5;
            return x;
        }
    }

    // Defing display function to display the whole queue
    void display(){
            for (int i = 0; i < 5; i++)
            {
                cout << arr[i] <<endl;
            }   
    }
};

// Testing the above functions:
int main()
{
    // Declaring an object to the class
    CircularQueue Q1;
    
    // A menu driven program to check all the defined functions in the class
    while (1)
    {
        cout << "1. Insert an element in the queue - enqueue" << endl;
        cout << "2. Delete element from the queue - Dequeue" << endl;
        cout << "3. Display items in the queue" << endl;
        cout << "4. To check whether the queue is empty or not" << endl;
        cout << "5. To check whether the queue is full or not" << endl;
        cout << "6. Exit" << endl;
        cout << "Enter your choice" << endl;
        int n;

        cin >> n;

        switch(n){
            case 1:
                int item;
                cout << "Enter the item" << endl;
                cin >> item;
                Q1.enqueue(item);
                break;

            case 2:
                if(!Q1.isEmpty()){
                    cout << "The dequeued value is: " << Q1.dequeue() << endl;
                }
                else{
                    cout << "The queue is empty" << endl;
                }

                break;

            case 3:
                cout << "The Queue is" << endl;
                Q1.display();
                break; 

            case 4:
                if(Q1.isEmpty()){
                    cout<<"Queue is Empty"<<endl;
                }
                else{
                    cout<<"Queue is not Empty"<<endl;
                }

            break;

            case 5:
                if(Q1.isFull()){                    
                    cout<<"Queue is Full"<<endl;
                }
                else{
                    cout<<"Queue is not Full"<<endl;
                }
            break;         

            case 6:
                exit(1);  

            default:
                cout << "Choose the options correctly";
                break;        
        }
    } 
    return 0;
}

/*
  Sample Input/Output:
  
  1. Insert an element in the queue - enqueue
  2. Delete element from the queue - Dequeue
  3. Display items in the queue
  4. To check whether the queue is empty or not
  5. To check whether the queue is full or not
  6. Exit
  Enter your choice
  1
  Enter the item
  10
  1. Insert an element in the queue - enqueue
  2. Delete element from the queue - Dequeue
  3. Display items in the queue
  4. To check whether the queue is empty or not
  5. To check whether the queue is full or not
  6. Exit
  Enter your choice
  1
  Enter the item
  20
  1. Insert an element in the queue - enqueue
  2. Delete element from the queue - Dequeue
  3. Display items in the queue
  4. To check whether the queue is empty or not
  5. To check whether the queue is full or not
  6. Exit
  Enter your choice
  3
  The Queue is
  10
  20
  0
  0
  0
  1. Insert an element in the queue - enqueue
  2. Delete element from the queue - Dequeue
  3. Display items in the queue
  4. To check whether the queue is empty or not
  5. To check whether the queue is full or not
  6. Exit
  Enter your choice
  2
  The dequeued value is: 10
  1. Insert an element in the queue - enqueue
  2. Delete element from the queue - Dequeue
  3. Display items in the queue
  4. To check whether the queue is empty or not
  5. To check whether the queue is full or not
  6. Exit
  Enter your choice
  2
  The dequeued value is: 20
  1. Insert an element in the queue - enqueue
  2. Delete element from the queue - Dequeue
  3. Display items in the queue
  4. To check whether the queue is empty or not
  5. To check whether the queue is full or not
  6. Exit
  Enter your choice
  4
  Queue is Empty
  1. Insert an element in the queue - enqueue
  2. Delete element from the queue - Dequeue
  3. Display items in the queue
  4. To check whether the queue is empty or not
  5. To check whether the queue is full or not
  6. Exit
  Enter your choice
  5
  Queue is not Full
  1. Insert an element in the queue - enqueue
  2. Delete element from the queue - Dequeue
  3. Display items in the queue
  4. To check whether the queue is empty or not
  5. To check whether the queue is full or not
  6. Exit
  Enter your choice
  6 
*/
/*
 The time complexities of different operations in a circular queue data structure are:-
  1) The time complexity of enqueue operation is O(1), that is constant time.
  2) The time complexity of dequeue operation is O(1), that is constant time. 
  3) The time complexity for checking whether the queue is empty of full is O(1), that is constant time.
  4) The time complexity of display function is O(n), where n is the number of Elements in the queue.
*/