private void cbo_MaThuoc_SelectedIndexChanged(object sender, EventArgs e)
{
string strsel = "select GiaBan from Thuoc where TenThuoc LIKE N'%" + cbo_MaThuoc.Text.Trim() + "%'";
SqlDataReader dr = conn.excuteReader(strsel);
while (dr.Read())
{
txt_DonGia.Text = dr["GiaBan"].ToString();
}
dr.Close();
conn.ClosedConnection();
}