//--- Display instructor coursrs in list private void listBox11_SelectedIndexChanged(object sender, EventArgs e) { Courses.Items.Clear(); Online_Exame ent = new Online_Exame(); //--get instractor from combo box string insName = Instructors.SelectedItem.ToString(); var insId = (int)(ent.Get_insid_by_inname(insName)).First(); label7.Text = "of" + " " + insName; //--get courses of same instructor var items = ent.get_instructor_course(insId); foreach (var i in items) { Courses.Items.Add(i); } }