public CartList addItem(CartList cl, int id, string t, decimal p)
    {
        Book b = new Book();

        b.BookID = id;
        b.Title  = t;
        b.Price  = p;
        int  q = 1;
        Cart c = new Cart(b, q);

        cl.add(c);
        CartList Cl = cl;

        return(Cl);
    }