C++ Program to Implement Circular Queue

A queue is an abstract data structure that contains a collection of elements. Queue implements the FIFO mechanism i.e the element that is inserted first is also deleted first.

A circular queue is a type of queue in which the last position is connected to the first position to make a circle.

A program to implement circular queue in C++ is given as follows −

Example

#include <iostream>
using namespace std;

int cqueue[5];
int front = -1, rear = -1, n=5;

void insertCQ(int val) {
   if ((front == 0 && rear == n-1) || (front == rear+1)) {
      cout<<"Queue Overflow \n";
      return;
   }
   if (front == -1) {
      front = 0;
      rear = 0;
   } else {
      if (rear == n - 1)
      rear = 0;
      else
      rear = rear + 1;
   }
   cqueue[rear] = val ;
}
void deleteCQ() {
   if (front == -1) {
      cout<<"Queue Underflow\n";
      return ;
   }
   cout<<"Element deleted from queue is : "<<cqueue[front]<<endl;

   if (front == rear) {
      front = -1;
      rear = -1;
   } else {
      if (front == n - 1)
      front = 0;
      else
      front = front + 1;
   }
}
void displayCQ() {
   int f = front, r = rear;
   if (front == -1) {
      cout<<"Queue is empty"<<endl;
      return;
   }
   cout<<"Queue elements are :\n";
   if (f <= r) {
      while (f <= r){
         cout<<cqueue[f]<<" ";
         f++;
      }
   } else {
      while (f <= n - 1) {
         cout<<cqueue[f]<<" ";
         f++;
      }
      f = 0;
      while (f <= r) {
         cout<<cqueue[f]<<" ";
         f++;
      }
   }
   cout<<endl;
}
int main() {

   int ch, val;
   cout<<"1)Insert\n";
   cout<<"2)Delete\n";
   cout<<"3)Display\n";
   cout<<"4)Exit\n";
   do {
      cout<<"Enter choice : "<<endl;
      cin>>ch;
      switch(ch) {
         case 1:
         cout<<"Input for insertion: "<<endl;
         cin>>val;
         insertCQ(val);
         break;

         case 2:
         deleteCQ();
         break;

         case 3:
         displayCQ();
         break;

         case 4:
         cout<<"Exit\n";
         break;
         default: cout<<"Incorrect!\n";
      }
   } while(ch != 4);
   return 0;
}

Output

The output of the above program is as follows −

1)Insert
2)Delete
3)Display
4)Exit

Enter choice : 1
Input for insertion:
Enter choice : 1
Input for insertion:
Enter choice : 1
Input for insertion:
Enter choice : 1
Input for insertion:
Enter choice : 1
Input for insertion:
Enter choice : 2
Element deleted from queue is : 5
Enter choice : 2
Element deleted from queue is : 3
Enter choice : 2
Element deleted from queue is : 2
Enter choice : 1
Input for insertion: 6
Enter choice : 3
Queue elements are :
7 9 6
Enter choice : 4
Exit