private void comboBox2_SelectedIndexChanged(object sender, EventArgs e) { comboBox3.Items.Clear(); textBox20.Clear(); textBox14.Clear(); textBox2.Clear(); comboBox3.Items.Add("Select Doctor"); comboBox3.Text = "Select Doctor"; if (comboBox2.Text != "Doctor Qualification") { PlaceAppointmentmysql DoctorsNames = new PlaceAppointmentmysql(); List <string> names = DoctorsNames.FindDoctorsNAMEbyqualification(comboBox2.Text); foreach (var item in names) { comboBox3.Items.Add(item.ToString()); comboBox3.Enabled = true; } } else { comboBox3.Enabled = false; } }