Queue in C++


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A queue is a linear dynamic data structure that follows First-In/First-Out (FIFO) principle. In a queue, addition of a new element and deletion of an element occurs at different end which implies that the element which is added first in the queue will be the first to be removed from the queue.

Features of queue

  • It is a dynamic data structure.
  • It has dynamic size.
  • It uses dynamic memory allocation.

Operations of a queue

  • isEmpty(): Checks whether the queue is empty or not.
  • size(): Returns the size of the queue.
  • frontElement(): Returns the front element of the queue. It is the element which will be dequeued next.
  • rearElement(): Returns the rear element of the queue. It is the element behind which next element will be enqueued.
  • EnQueue(x): Adds a new element ‘x’ from the rear side of the queue. Consequently, size of the queue increases by 1.
  • Queue EnQueue
  • DeQueue(): Deletes the front element of the queue. Consequently, size of the queue decreases by 1.
  • Queue DeQueue

Implementation of queue

#include <iostream>
using namespace std;

#define MAX 100 
class CreateQueue {
  int front;
  int rear;

  public:
  //assigning MAX size of the queue
  int queue[MAX];

  CreateQueue() {
    rear = -1;
    front = -1;
  }

  void isEmpty();
  int size();
  void EnQueue(int x);
  void DeQueue();
  int frontElement();
  int rearElement();
};

  // create a function to check whether 
  // the queue is empty or not  
  void CreateQueue::isEmpty() {
    if(rear == front) {
      cout<<"Queue is empty."<<"\n";
    } else {
      cout<<"Queue is not empty."<<"\n";
    }
  }

  //create a function to return size of the queue 
  int CreateQueue::size() {
     return (rear - front);
  } 

  //create a function to add new element       
  void CreateQueue::EnQueue(int x){
    if(rear == (MAX - 1)){
      cout<<"Queue size limit reached."<<"\n";
    } else {
      queue[++rear] = x;
      cout<<x<<" is added into the queue."<<"\n";
    }
  }

  //create a function to delete front element       
  void CreateQueue::DeQueue(){
    if(rear == front){
      cout<<"Queue is empty."<<"\n";
    } else {
      int x = queue[++front];
      cout<<x<<" is deleted from the queue."<<"\n";
    }
  }  

  //create a function to get front element       
  int CreateQueue::frontElement() {
    if(rear == front) {
      cout<<"Queue is empty."<<"\n";
      return 0;
    } else {
      return queue[front+1];
    }
  }

  //create a function to get rear element       
  int CreateQueue::rearElement() {
    if(rear == front) {
      cout<<"Queue is empty."<<"\n";
      return 0;
    } else {
      return queue[rear];
    }
  }

// test queue implementation code 
int main() {
  class CreateQueue MyQueue;
  MyQueue.EnQueue(10);
  MyQueue.EnQueue(20);
  MyQueue.EnQueue(30);
  MyQueue.EnQueue(40);

  MyQueue.DeQueue();
  MyQueue.isEmpty();
  return 0; 
}

Output

10 is added into the queue.
20 is added into the queue.
30 is added into the queue.
40 is added into the queue.
10 is deleted from the queue.
Queue is not empty.
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