Circular Linked List Program in C

Implementation

Circular Linked List is a variation of Linked list in which the first element points to the last element and the last element points to the first element. Both Singly Linked List and Doubly Linked List can be made into a circular linked list.

C Implementation

The C Code to demonstrate the circular linked list operations is given below −

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>
struct node {
   int data;
   int key;
   struct node *next;
};
struct node *head = NULL;
struct node *current = NULL;
bool isEmpty(){
   return head == NULL;
}
int length(){
   int length = 0;

   //if list is empty
   if(head == NULL) {
      return 0;
   }
   current = head->next;
   while(current != head) {
      length++;
      current = current->next;
   }
   return length;
}

//insert link at the first location
void insertFirst(int key, int data){

   //create a link
   struct node *link = (struct node*) malloc(sizeof(struct node));
   link->key = key;
   link->data = data;
   if (isEmpty()) {
      head = link;
      head->next = head;
   } else {

      //point it to old first node
      link->next = head;

      //point first to new first node
      head = link;
   }
}

//delete first item
struct node * deleteFirst(){

   //save reference to first link
   struct node *tempLink = head;
   if(head->next == head) {
      head = NULL;
      return tempLink;
   }

   //mark next to first link as first
   head = head->next;

   //return the deleted link
   return tempLink;
}

//display the list
void printList(){
   struct node *ptr = head;
   printf("\n[ ");

   //start from the beginning
   if(head != NULL) {
      while(ptr->next != ptr) {
         printf("(%d,%d) ",ptr->key,ptr->data);
         ptr = ptr->next;
      }
   }
   printf(" ]");
}
int main(){
   insertFirst(1,10);
   insertFirst(2,20);
   insertFirst(3,30);
   insertFirst(4,1);
   insertFirst(5,40);
   insertFirst(6,56);
   printf("Original List: ");

   //print list
   printList();
   while(!isEmpty()) {
      struct node *temp = deleteFirst();
      printf("\nDeleted value:");
      printf("(%d,%d) ",temp->key,temp->data);
   }
   printf("\nList after deleting all items: ");
   printList();
}

Output

Original List: 
[ (6,56) (5,40) (4,1) (3,30) (2,20)  ]
Deleted value:(6,56) 
Deleted value:(5,40) 
Deleted value:(4,1) 
Deleted value:(3,30) 
Deleted value:(2,20) 
Deleted value:(1,10) 
List after deleting all items: 
[  ]