public bool checkLogin(string txtName, string txtPass, db_csDataSet dts)
        {
            DataTable dt = new DataTable();

            if (dts.user.Count() > 0)
            {
                dt = dts.Tables["User"];
                var q = from qds in dt.AsEnumerable()
                        where qds.Field <string>("user_id").ToString().Trim() == txtName.ToString().Trim() &&
                        qds.Field <string>("user_password").ToString().Trim() == txtPass.ToString().Trim()
                        select new
                {
                    userID   = qds.Field <string>("user_id").ToString(),
                    userpass = qds.Field <string>("user_password").ToString()
                };
                if (q.Count() <= 0)
                {
                    return(false);
                }
                else
                {
                    return(true);
                }
            }
            else
            {
                return(false);
            }
        }
        private void button1_Click(object sender, EventArgs e)
        {
            Controler    c      = new Controler();
            bool         resLog = false;
            db_csDataSet ds     = db_csDataSet;

            resLog = c.checkLogin(textBox1.Text, textBox2.Text, ds);
            if (resLog)
            {
                Form1 frm1 = new Form1();
                frm1.ShowDialog();
                frm1.Activate();
                this.Hide();
                this.Close();
            }
            else
            {
                MessageBox.Show("กรุณากรอกข้อมูลให้ถูกต้อง", "ข้อมูลไม่ถูกต้อง", MessageBoxButtons.OK, MessageBoxIcon.Error);
                textBox1.Text = "";
                textBox2.Text = "";
                textBox1.Focus();
            }
        }