public static void CheckList()
        {
            Console.Clear();
            Console.WriteLine("You are working in the \"{0}.xml\" file\n\n", fileName);
            Console.WriteLine("1) List all books.");
            Console.WriteLine("2) Add a book.");
            Console.WriteLine("3) Save and exit.");

            int userValue = Vaildation.IsInt(Console.ReadLine(), "Number please");

            switch (userValue)
            {
            case (int)(UserOptions.listOfBooks):
                CardCatalog.ListBooks(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments) + "//" + fileName + ".xml", CardCatalog.myBooks);
                break;

            case (int)(UserOptions.addBook):
                CardCatalog.AddBook(CardCatalog.myBooks);
                break;

            case (int)(UserOptions.saveAndExit):
                CardCatalog.SaveAndExit();
                break;

            default:
                Console.Clear();
                Console.WriteLine("Invalid number. Please enter 1, 2, or 3.");
                CheckList();
                break;
            }
        }
        public static void AddBook(List <Book> books)
        {
            Console.Clear();

            Console.Write("Enter book title: ");
            string title = Console.ReadLine();

            Console.Write("Enter author name: ");
            string author = Console.ReadLine();

            Console.Write("Enter publishing year: ");
            int yearPublished = Vaildation.IsInt(Console.ReadLine(), "publishing year again");

            Console.Write("Enter price: ");
            decimal price = Vaildation.IsDecimal(Console.ReadLine());

            books.Add(new Book()
            {
                Title = title, Author = author, YearPublished = yearPublished, Price = price
            });

            addBookCount++;
            Console.WriteLine("You added {0} book(s).", addBookCount);
            Console.Write("Do you want add another book? (Y/N)");
            if (Vaildation.IsYorN(Console.ReadLine()))
            {
                AddBook(books);
            }

            Program.CheckList();
        }