Adding the circular queue (#104)

* Create circular-queue-linked-list.cpp

* Update README.md

* Update circular-queue-linked-list.cpp

queues/README.md

@@ -3,3 +3,4 @@
 ### C or C++
 
 1. [Queue using linked list](c-or-cpp/queue-linked-list.cpp)
+2. [Circular Queue using linked list](c-or-cpp/circular-queue-linked-list.cpp)

queues/c-or-cpp/circular-queue-linked-list.cpp

@@ -0,0 +1,109 @@
+// Content: Circular Queue using linked list
+// Author: Tawfik Yasser
+// Date: Mon, 8 Mar 2021
+#include <iostream>
+using namespace std;
+class Node
+{
+public:
+    int data;
+    Node *next;
+    Node() {}
+};
+class QueueLL
+{
+private:
+    Node *front;
+    Node *rear;
+    int length;
+public:
+    QueueLL()
+    {
+        front = rear = NULL; length = 0;
+    }
+    //Function to add new element in the queue
+    void enqueue(int value)
+    {
+        Node *newNode = new Node();
+        newNode->data = value;
+        newNode->next = NULL;
+        if(rear == NULL)
+        {
+            front = rear = newNode;
+            rear->next = front;
+        }
+        else
+        {
+            rear->next = newNode;
+            rear = newNode;
+            rear->next = front;
+        }
+      length++;
+    }
+    //Function to remove element from the queue
+    void dequeue()
+    {
+        Node *temp = front;
+        if(front == NULL && rear == NULL){
+            cout<<"Empty Queue"<<endl;
+        }else if(front == rear){
+            front = rear = NULL;
+            delete temp;
+        }else{
+            front = temp->next;
+            rear->next = front;
+            delete temp;
+        }
+      length--;
+        if(length < 0 )
+            length = 0;
+    }
+  //Function returns the first element in the queue
+    void peek()
+    {
+        if(front == NULL && rear == NULL){
+            cout<<"Empty Queue"<<endl;
+        }else{
+            cout<<front->data<<endl;
+        }
+    }
+  //Function to display all the elements in the queue
+    void print()
+    {
+        if(front == NULL && rear == NULL)
+        {
+            cout<<"Empty Queue"<<endl;
+        }
+        else
+        {
+            Node *temp = front;
+            while(temp->next != front)
+            {
+                cout<<"[ "<<temp->data<<" ] ";
+                temp = temp->next;
+            }
+            cout<<"[ "<<temp->data<<" ] ";
+        }
+    }
+    int _size()
+    {
+        return length;
+    }
+};
+int main()
+{
+    QueueLL qll;
+    qll.enqueue(5);
+    qll.enqueue(3);
+    qll.enqueue(-2);
+    qll.print();
+    cout<<endl;
+    cout<<"Queue size = "<<qll._size()<<endl;
+    qll.peek();
+    qll.dequeue();
+    qll.print();
+    cout<<endl;
+    cout<<"Queue size = "<<qll._size()<<endl;
+    qll.peek();
+    return 0;
+}