ช่วยสอนการเขียนโปรโมชั่นซื้อ1แถม1ให้หน่อยคับ. มือใหม่

 private void textBox1_TextChanged(object sender, EventArgs e)
        {
            DataTable cashier1 = ConnectionStr.executsql("Select * From Tbl_ProductEventData Where Barcode = '" + textBox1.Text + "'");
            DataTable freeselect = ConnectionStr.executsql("Select * From Tbl_GetFree Where Main_barcode ='" + textBox1.Text + "'");
            try
            {
                if (radioButton1.Checked)
                {
                    for (int i = 0; i <= dataGridView1.Rows.Count - 1; i++)
                    {
                        string barcode = dataGridView1.Rows[i].Cells[0].Value.ToString();
                        string qty = dataGridView1.Rows[i].Cells[2].Value.ToString();
                        DataTable check = ConnectionStr.executsql("Select Main_barcode,Main_pro_qty From Tbl_GetFree Where Main_barcode='" + barcode + "' AND Main_qty = '" + qty + "' ");
                        if(freeselect.Rows.Count>0 && check.Rows.Count > 0)
                        {
                            textBox2.Text = freeselect.Rows[0][6].ToString();
                            textBox3.Text = freeselect.Rows[0][16].ToString();
                            textBox3.Text = Convert.ToDouble(textBox3.Text).ToString("##,##0.00");
                        }
                        else
                        {

                        }
                    }
                }
                else if (radioButton2.Checked)
                {
                    textBox2.Text = cashier1.Rows[0][1].ToString();
                    textBox3.Text = cashier1.Rows[0][11].ToString();
                    textBox3.Text = Convert.ToDouble(textBox3.Text).ToString("##,##0.00");
                }
                
                else
                {




                }
            }
            catch
            {

            }
            

        }