private void tabControl1_SelectedIndexChanged(object sender, EventArgs e)
        {
            cmboBook.Items.Clear();
            List <string> book = DBConnection.cmboBook();

            cmboBook.Items.AddRange(book.ToArray());
        }
        private void AlterBooksForm_Load(object sender, EventArgs e)
        {
            lblEmployeeName.Text = "Welcome " + employee.FullName;
            List <string> book = DBConnection.cmboBook();

            listDisplay.HorizontalScrollbar = true;
            cmboBook.Items.AddRange(book.ToArray());
            cmboCategory.Items.AddRange(DBConnection.getCategorie().ToArray());
            cmboCategory.SelectedIndex = 0;
            book = null;
        }