C++ Program to Implement Circular Singly Linked List

Circular singly linked list is a type of data structure that is made up of nodes that are created using self referential structures. Each of these nodes contain two parts, namely the data and the reference to the next list node.

Only the reference to the first list node is required to access the whole linked list. This is known as the head. The last node in the list points to head or first node of the list. That is the reason this is known as a circular linked list.

A program to implement circular singly linked list is given as follows.

Example

 Live Demo

#include <iostream>
using namespace std;
struct Node {
   int data;
   struct Node *next;
};
struct Node* head = NULL;
void insert(int newdata) {
   struct Node *newnode = (struct Node *)malloc(sizeof(struct Node));
   struct Node *ptr = head;
   newnode->data = newdata;
   newnode->next = head;
   if (head!= NULL) {
      while (ptr->next != head)
      ptr = ptr->next;
      ptr->next = newnode;
   } else
   newnode->next = newnode;
   head = newnode;
}
void display() {
   struct Node* ptr;
   ptr = head;
   do {
      cout<<ptr->data <<" ";
      ptr = ptr->next;
   } while(ptr != head);
}
int main() {
   insert(3);
   insert(1);
   insert(7);
   insert(2);
   insert(9);
   cout<<"The circular linked list is: ";
   display();
   return 0;
}

Output

The circular linked list is: 9 2 7 1 3

In the above program, the structure Node forms the linked list node. It contains the data and a pointer to the next linked list node. This is given as follows.

struct Node {
   int data;
   struct Node *next;
};

The function insert() inserts the data into the beginning of the linked list. It creates a newnode and inserts the number in the data field of the newnode. If the head is NULL, then newnode points to itself otherwise the last node in the circular linked list points to newnode. Then the head points to the start of the list i.e. to the newnode. This is given below.

void insert(int newdata) {
   struct Node *newnode = (struct Node *)malloc(sizeof(struct Node));
   struct Node *ptr = head;
   newnode->data = newdata;
   newnode->next = head;
   if (head!= NULL) {
      while (ptr->next != head)
      ptr = ptr->next;
      ptr->next = newnode;
   } else
   newnode->next = newnode;
   head = newnode;
}

The function display() displays the whole linked list. First ptr points to head. Then it is continuously forwarded to the next node until all the data values of the nodes are printed. This is given below.

void display() {
   struct Node* ptr;
   ptr = head;
   do {
      cout<< ptr->data <<" ";
      ptr = ptr->next;
   } while(ptr != head);
}

In the function main(), first various values are inserted into the circular linked list by calling insert(). Then the linked list is displayed. This is given below.

int main() {
   insert(3);
   insert(1);
   insert(7);
   insert(2);
   insert(9);
   cout<<"The circular linked list is: ";
   display();
   return 0;
}