void deleteBook(book_t **head)
{
   char titleToDelete[50];
    printf("Podaj tytul ksiazki, ktora chcesz usunac. \n");
    gets(titleToDelete);

    book_t * current = *head;
    book_t * tmp_book = NULL;
    if(strcasecmp(current->title, titleToDelete)==0){
         tmp_book = (*head)->next;
    free(*head);
    *head = tmp_book;
    } else {
        while(current->next!=NULL && strcasecmp(current->next->title, titleToDelete)!=0 ){
            current=current->next;
        }
        if(strcasecmp(current->next->title, titleToDelete)==0){
                        tmp_book = current->next;
    current->next = tmp_book->next;
    free(tmp_book);
        }



    }
}