void saveToFile (book_t * head){
  FILE *fp;
  fp = fopen ("Books.csv", "w");
    if(fp==NULL)
    {
        printf("Nie można zapisac zaaktualizowanej listy.\n");
    }
  book_t *current = head;

  while (current != NULL){

      fprintf (fp, "%s;", current->title);
      fprintf (fp, "%d;", current->pages);
      fprintf (fp, "%d;", current->yearOfRelease);
      fprintf (fp, "%s;", current->date);
      fprintf (fp, "%s;", current->borrower->name);
      fprintf (fp, "%s;", current->borrower->surname);
      author_t *curr_author = current->author;
      while (curr_author != NULL){
      fprintf (fp, "%s;", curr_author->name);
      fprintf (fp, "%s", curr_author->surname);
      if (curr_author->next != NULL){
          fprintf (fp, ";");
        }
      curr_author = curr_author->next;
    }
      current = current->next;
    }


  fclose (fp);
}