private void teacherSelect_SelectedIndexChanged(object sender, EventArgs e) { totalhrstxt.Text = ""; chrgtxt.Text = ""; KeyValuePair <int, string> selectEntry = (KeyValuePair <int, string>)teacherSelect.SelectedItem; string tID = selectEntry.Key.ToString(); idtxt.Text = tID; slr = new Salary(); slr.CalculateTotalHrs(tID); totalhrstxt.Text = slr.TotalNoHrs.ToString(); }