private static void UpdatingBook()
        {
            BookListHolder.ShowAllBooks();

            Console.WriteLine("-------------");

            Console.WriteLine("Enter the number of the book you want to change/update");
            int enteredNum = Convert.ToInt32(Console.ReadLine());

            Console.WriteLine("The selected book is below");
            Console.WriteLine(BookListHolder.bookList[enteredNum - 1].Title + " ~ " + BookListHolder.bookList[enteredNum - 1].Author + " ~ " + BookListHolder.bookList[enteredNum - 1].Year);

            Console.WriteLine("Enter the Title of the new Book");
            string newTitle = Console.ReadLine();

            Console.WriteLine("Enter the Author of the new Book");
            string newAuthor = Console.ReadLine();

            Console.WriteLine("Enter the Year of the new Book");
            int newYear = Convert.ToInt32(Console.ReadLine());

            BookListHolder.bookList[enteredNum - 1].Title  = newTitle;
            BookListHolder.bookList[enteredNum - 1].Author = newAuthor;
            BookListHolder.bookList[enteredNum - 1].Year   = newYear;

            Console.WriteLine("The book '" + newTitle + "' is successfully updated");
            Console.WriteLine("");
        }
        //showing all books and providing choices
        public static void MainMenuChoices()
        {
            BookListHolder.ShowAllBooks();

            Console.WriteLine("----------------------");
            Console.WriteLine("1. Buy a book");
            Console.WriteLine("2. Remove a book");
            Console.WriteLine("3. Update/Change a book");
            Console.WriteLine("");
            Console.WriteLine("Enter the number of the operation you want to carry out");
            // managing the user's choice
            int enteredOperation = Convert.ToInt32(Console.ReadLine());

            switch (enteredOperation)
            {
            case 1:
                BuyingBook();
                break;

            case 2:
                RemovingBook();
                break;

            case 3:
                UpdatingBook();
                break;

            default:
                Console.WriteLine("Incorrect Operation!!!!!!!!!!");
                break;
            }
            Console.WriteLine("");
            MainMenuChoices();
        }
        // removing a book
        private static void RemovingBook()
        {
            BookListHolder.ShowAllBooks();

            Console.WriteLine("-------------");

            Console.WriteLine("Enter the number of the book you want to remove");
            int enteredNum = Convert.ToInt32(Console.ReadLine());

            Console.WriteLine("Book '" + BookListHolder.bookList[enteredNum - 1].Title + "' is successfully removed");

            BookListHolder.bookList.Remove(BookListHolder.bookList[enteredNum - 1]);

            Console.WriteLine("");
        }