private void button3_Click(object sender, EventArgs e)
        {
            searchBooks sb = new searchBooks();

            if (sb.ShowDialog() == DialogResult.OK)
            {
                isEdit           = true;
                btAddorEdit.Text = "Редактировать";

                tbAuthor.Text = sb.pAuthor;
                tbTitle.Text  = sb.pTitle;
                tbYear.Text   = sb.pYear;
                tbIsbn.Text   = sb.pIsbn;
                bookId        = sb.pBookID;
            }
            else
            {
                isEdit           = false;
                btAddorEdit.Text = "Добавить";

                tbAuthor.Text = "";
                tbTitle.Text  = "";
                tbYear.Text   = "";
                tbIsbn.Text   = "";
            }
        }
        private void bt_searchBook_Click(object sender, EventArgs e)
        {
            searchBooks sb = new searchBooks();

            if (sb.ShowDialog() == DialogResult.OK)
            {
                tb_bookAuthor.Text = sb.pAuthor;
                tbBookTitle.Text   = sb.pTitle;
                tb_bookYear.Text   = sb.pYear;
                bookId             = sb.pBookID;
                book_isbn          = sb.pIsbn;
            }
        }