private void txtDay_TextChanged(object sender, EventArgs e) { try { int day = int.Parse(txtDay.Text); int txtmonth = int.Parse(txtMonth.Text); int txtyear = int.Parse(txtYear.Text); int maxDay = DateTime.DaysInMonth(txtyear, 2); IEnumerable <int> month = TimekeepingBO.Month(day); txtMonth.Items.Clear(); txtMonth.Text = txtMonth.Text; foreach (var item in month) { txtMonth.Items.Add(item); } if (maxDay < int.Parse(txtDay.Text)) { txtMonth.Items.Remove(2); } } catch { } }