C语言在单链表中查找数据项

#include <stdio.h>
#include <stdlib.h>

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

struct node *head = NulL;
struct node *current = NulL;

//Create linked List
voID insert(int data) {
   // Allocate memory for new node;
   struct node *link = (struct node*) malloc(sizeof(struct node));

   link->data = data;
   link->next = NulL;

   // If head is empty, create new List
   if(head==NulL) {
      head = link;
      return;
   }

   current = head;

   // move to the end of the List
   while(current->next!=NulL)
      current = current->next;

   // Insert link at the end of the List
   current->next = link; 
}

voID find_data(int item) {
   int pos = 0;

   if(head==NulL) {
      printf("linked List not initialized");
      return;
   } 

   current = head;
   while(current->next!=NulL) {
      if(current->data == item) {
         printf("%d found at position %d\n", item, pos);
         return;
      }

      current = current->next;
      pos++;
   }

   printf("%d does not exist in the List", item);
}

int main() {
   insert(10);
   insert(20);
   insert(30);
   insert(1);
   insert(40);
   insert(56); 

   find_data(40);
   find_data(44);

   return 0;
}