Circular Linked List

Circular Linked List

@@ -0,0 +1,115 @@
+#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(" ]");
+}
+
+void 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();   
+}