lab 6-2 nosure

#include<stdio.h>
struct listnode {
  int data;
  struct listnode *next;
};

typedef struct listnode LN;

void insert_at_front(LN **hptr, int d);
void print(LN *head);
int sum(LN *head);
LN *find_tail(LN *head);

int main(){
  LN *head;
  head = NULL;
  int d;
  printf("Enter data: ");
  do{
    scanf("%d", &d);
    if(d > 0){
        insert_at_back(&head,d);
    }
  }while(d > 0);
    printf("=");
    print(head);
    printf("\n=%d", sum(head));
  return 0;
}

void insert_at_back(LN **hptr, int d){
    LN *new_node = (LN*)malloc(sizeof(LN));
    LN *tail;
    new_node->data=d;
    new_node->next=NULL;
    tail=find_tail(*hptr);
    if(tail==NULL)
        *hptr=new_node;
    else
        tail->next=new_node;

}
void print(LN *head){
        while(head!=NULL){
            printf("%d ",head->data);
            head=head->next;
          }
}

int sum(LN *head){
        int num=0;
        while(head!=NULL){
            num=num+head->data;
            head=head->next;
        }
        return num;
}
LN *find_tail(LN *head){
    LN *tail;
    if(head==NULL)
        return NULL;
    tail=head;
    while(tail->next!=NULL){
        tail=tail->next;
    }
    return tail;
}