Circular Linked List

//Circular linked list

#include <stdio.h>
#include <iostream>
using namespace std;

struct ListNode{
    int data;
    struct ListNode *next = NULL;
};

int ListLength(struct ListNode *head){
    int count=0;
    struct ListNode *curr=head;
       
    if(head==NULL)
        return 0;
    
   do{  printf("%d", curr->data);
        curr = curr->next;
        count++;
    } while(curr!=head);
    
    return count;    
}

void InsertAtEndCLL(struct ListNode **ptrtohead, int data){
    struct ListNode *newnode = (ListNode *)malloc(sizeof(ListNode));
    newnode->data = data;
    struct ListNode *head,*curr;
    head=*ptrtohead;
    curr=head;
    
    if(head==NULL)
       {
        *ptrtohead = newnode;
        newnode->next=newnode;
        return;
       }
    
    while(curr->next!=head)
        curr = curr->next;
    
    curr->next=newnode;
    newnode->next = head;    
}

void InsertAtStartCLL(struct ListNode **ptrtohead, int data){
    struct ListNode *newnode = (ListNode *)malloc(sizeof(ListNode));
    newnode->data = data;
    struct ListNode *head,*curr;
    head=*ptrtohead;
    curr=head;
    
    if(head==NULL)
       {
        *ptrtohead = newnode;
        newnode->next=newnode;
        return;
       }
    
    while(curr->next!=head)
        curr = curr->next;
    
    curr->next=newnode;
    newnode->next = head;
    
    //relocating head
    *ptrtohead = newnode;    
}

void DeleteEndNodeCLL(struct ListNode **ptrtohead){
    struct ListNode *head,*curr,*prevcurr;
    head=*ptrtohead;
    curr=head;
    
    if(head==NULL)
       {
        printf("No node to delete");
        return;
       }
    
    if(head->next==head){
        free(head);
        *ptrtohead = NULL;
        return;
    }
    
    while(curr->next!=head){
        prevcurr=curr;
        curr = curr->next;
    }
    
    prevcurr->next=head;
    free(curr);   
}

void DeleteStartNodeCLL(struct ListNode **ptrtohead){
    
    struct ListNode *head,*curr,*prevcurr;
    head=*ptrtohead;
    curr=head;
    
    if(head==NULL)
       {
        printf("No node to delete");
        return;
       }
    
    if(head->next==head){
        free(head);
        *ptrtohead = NULL;
        return;
    }
    
    //shift head one node forward,reinitialize pointers and then delete end node;
    *ptrtohead = head->next;
    head = head->next;
    curr=head;
    
    while(curr->next!=head){
        prevcurr=curr;
        curr = curr->next;
    }
    
    prevcurr->next=head;
    free(curr);    
    
}

int main() {
    //creating a circular linked list
	struct ListNode *a,*b,*c,*head, *curr;
    a = (ListNode *)malloc(sizeof(ListNode));
    b = (ListNode *)malloc(sizeof(ListNode));
    c = (ListNode *)malloc(sizeof(ListNode));
    a->next = b;
    b->next = c;
    c->next = a;
    
    a->data = 1;
    b->data = 2;
    c->data =4;
    head=a;
    
    //head=NULL;
    //InsertAtEndCLL(&head,5);
    //InsertAtStartCLL(&head,5);
    //DeleteEndNodeCLL(&head);
   DeleteStartNodeCLL(&head);
    
   int count = ListLength(head);
   printf("\nCount:%d", count); 
   return 0;
}