Introduction to Circular linked list

// Linked List in C Implementation code
#include <stdio.h>
#include <stdlib.h>

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

void insertStart (struct Node **head, int data)
{
  struct Node *newNode = (struct Node *) malloc (sizeof (struct Node));
  newNode->data = data;

  // if its the first node being entered
  if (*head == NULL)
    {
      *head = newNode;
      (*head)->next = *head;
      return;
    }

  // if LL already as >=1 node
  struct Node *curr = *head;

  // traverse till last node in LL
  while (curr->next != *head)
    {
      curr = curr->next;
    }
  // assign LL's last node's next as this new node
  curr->next = newNode;

  // assign newNode's next as current head
  newNode->next = *head;

  // change head to this new node
  *head = newNode;
}

void display (struct Node *head)
{
  // if there are no node in LL
  if (head == NULL)
    return;

  struct Node *temp = head;

  //need to take care of circular structure of LL
  do
    {
      printf ("%d ", temp->data);
      temp = temp->next;

    }
  while (temp != head);
  printf ("\n");
}

int main ()
{

  struct Node *head = NULL;

  printf ("Linked List: ");
  insertStart (&head, 6);
  insertStart (&head, 5);
  insertStart (&head, 4);
  insertStart (&head, 3);
  insertStart (&head, 2);
  insertStart (&head, 1);
  display (head);

  return 0;
}

#include <bits/stdc++.h>
using namespace std;

struct Node { 
    int data; 
    struct Node* next; 
    // Pointer pointing towards next node
};

void insertFront (struct Node **head, int data)
{

  // dynamically create memory for this newNode
  struct Node *newNode = (struct Node *) malloc (sizeof (struct Node));

  // assign data value
  newNode->data = data;
  // change the next node of this newNode 
  // to current head of Linked List
  newNode->next = *head;

  //re-assign head to this newNode
  *head = newNode;
}

void display (struct Node *node)
{
  cout << "\n";
  // as linked list will end when Node is Null

  while (node != NULL)
    {
      cout << node->data << " "; node = node->next;
    }
}

int main ()
{
  struct Node *head = NULL;

  // Need '&' i.e. address as we need to change head
  insertFront (&head, 6);
  insertFront (&head, 12);
  insertFront (&head, 18);
  insertFront (&head, 24);
  insertFront (&head, 30);

cout << "the linked list is" << endl;  
display (head); 
  return 0;
}

import java.lang.*;

class LinkedList {
    Node head;
    // not using parameterized constructor would by default
    // force head instance to become null
    // Node head = null;  // can also do this, but not required

    // Node Class
    class Node{
        int data;
        Node next;

        Node(int x) // parameterized constructor
        {
            data = x;
            next = null;
        }
    }
    public Node insert(int data)
    {
        // Creating newNode memory & assigning data value
        Node newNode = new Node(data);
        // assigning this newNode's next as current head node
        newNode.next = head;

        // re-assigning head to this newNode
        head = newNode;

        return head;
    }


    public void display()
    {
        Node node = head;
        //as linked list will end when Node reaches Null
        while(node!=null)
        {
            System.out.print(node.data + " ");
            node = node.next;
        }
        System.out.println();
    }
}
class Main{	 
public static void main(String args[])
    {
        LinkedList ll = new LinkedList();

        ll.insert(6);
        ll.insert(5);
        ll.insert(3);
        ll.insert(4);
        ll.insert(2);
        ll.insert(1);

        ll.display();

    }
}

Output

1 2 4 3 5 6