Text box and data grid view

private void textBox3_KeyPress(object sender, KeyPressEventArgs e)
       {
            if (e.KeyChar==(char)13)
            {
                string y = textBox3.Text;
                string sql = "SELECT * FROM item_data where stock_code='" + textBox3.Text + "'";
                cmd = new SqlCommand(sql, con);

                for (int i = 0; i < dataGridView1.Rows.Count; i++)
                {
                    if (dataGridView1.Rows[i].Cells[0].Value != null)
                    {
                        if (dataGridView1.Rows[i].Cells[0].Value.ToString() == y)
                        {

                                //total =0;
                                quantity1++;
                                //total = price1+price;
                               // price = total;
                                //total1 = total1+total;
                                //textBox2.Text = total1.ToString ();
                                dataGridView1.Rows[i].Cells[4].Value = quantity1;
                               // dataGridView1.Rows[i].Cells[3].Value = price;
                             //   textBox2.Text =price .ToString ();
                                break;
                        }




                    }
                        else
                        {
                            try
                            {
                                con.Open();
                                dr = cmd.ExecuteReader();
                                if (dr.Read())
                                {
                                    int stock_code = (int)dr["stock_code"];
                                    string description = (string)dr["descriptionOfItem"];
                                    price = (int)dr["selling_price"];
                                    quantity = (int)dr["quantity"];
                                    string name = (string)dr["name"];
                                    string stock_date = (string)dr["stock_date"];
                                    stock_code.ToString();
                                    price.ToString();
                                    quantity.ToString();
                                    con.Close();

                                    ///////////////////////checking if there's still items in the database/////////////////////////
                                    
                                    if (quantity >= 1)
                                    {
                                        string sql1 = "update item_data set quantity=quantity-1 where stock_code='" + textBox3.Text + "'";
                                        cmd = new SqlCommand(sql1, con);
                                        try
                                        {
                                            con.Open();
                                            cmd.ExecuteNonQuery();
                                            row = new string[] { stock_code.ToString(), description, price.ToString(), quantity1.ToString(), name.ToString(), stock_date };
                                            //                    row = new string[] { b, contact, c, d };
                                            dataGridView1.Rows.Add(stock_code.ToString(), description, name.ToString(), price.ToString(), quantity1.ToString(), stock_date);
                                            //    dataGridView1.CurrentRow.Cells[4].Value = x;
                                            price1 = price;
                                   //         textBox2.Text = price.ToString ();
                                            con.Close();
                                        }
                                        catch (Exception ex)
                                        {
                                            MessageBox.Show(ex.ToString());
                                            con.Close();
                                        }
                                    }

                                    else
                                    {
                                        con.Close();
                                    }
                                }
                                else
                                    con.Close();
                            }
                            catch (Exception ex)
                            {
                                MessageBox.Show(ex.ToString());
                                con.Close();
                            }
                        }
                    }
       /*         */
            }
            
       amount();
       }
public void amount()
        {
            for (int i = 0; i < dataGridView1.Rows.Count; i++)
            {
                if (dataGridView1.Rows[i].Cells[0].Value != null)
                {
                    if (dataGridView1.Rows[i].Cells[3].Value != null && dataGridView1.Rows[i].Cells[4].Value != null)
                    {
                        p1 = dataGridView1.Rows[i].Cells[3].Value.ToString();
                        q1 = dataGridView1.Rows[i].Cells[4].Value.ToString();
                        p = Convert.ToInt32(p1);
                        q = Convert.ToInt32(q1);
                        t = t + price;
                        t1 = t1 + t;
                        textBox2.Text = t1.ToString();
                        break;
                    }
                }
            }
        }