private void addBook_Load(object sender, EventArgs e) { lc.getAuthorAndCategory(out dt1, out dt2); categorycb.DataSource = dt1; categorycb.ValueMember = dt1.Columns[0].ToString(); categorycb.DisplayMember = dt1.Columns[1].ToString(); authorcb.DataSource = dt2; authorcb.ValueMember = dt2.Columns[0].ToString(); authorcb.DisplayMember = dt2.Columns[1].ToString(); }