Im tyring 2day to solve this problem

 rivate void btnOk_Click(object sender, EventArgs e)
        {
            if (txtBarCode.Text == "" || txtProductName.Text == "" || txtPrice.Text == "" || numericUpDown1 == null)
            {

                MessageBox.Show("Please Fill", "Warning", MessageBoxButtons.OK, MessageBoxIcon.Warning);

                this.Show();
                txtBarCode.Focus();
                return;
            }
            try
            {
                decimal price = Convert.ToDecimal(txtPrice.Text);
                decimal awd;
                awd = price - ((price * 18) / 100);

                Program.AddProduct(txtBarCode.Text, txtArtNumber.Text, txtProductName.Text, txtPrice.Text, txtComment.Text, numericUpDown1.Value, awd.ToString(), txtSelfPrice.Text);

                Inventary inv = new Inventary();
                inv.save();
                DialogResult = DialogResult.OK;
            }
            catch (Exception ex)
            {

                MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
            }
            Inventary inv = new Inventary();
            inv.load();
            this.Close();
        }

internal static void EditProduct(string txtBarCode, string txtArtNumber, string txtProductName, string txtPrice, string txtComment, decimal NumericUpDown1, string PriceWithOutAWD, string txtSelfPrice) 
        {
            SqlConnection con = new SqlConnection(ConnectionString);
            SqlCommand cmd = new SqlCommand("UPDATE Products SET BarCode = @BarCode, ArtNumber = @ArtNumber, ProductName = @ProductName, Price = @Price, SelfPrice = @SelfPrice, PriceWithOutAWD = @PriceWithOutAWD, UnitsInStock = @UnitsInStock, Comment = @Comment WHERE BarCode = @bc AND ArtNumber = @an ", con);

            
            cmd.Parameters.Add(new SqlParameter("@BarCode", txtBarCode));
            cmd.Parameters.Add(new SqlParameter("@ArtNumber", txtArtNumber));
            cmd.Parameters.Add(new SqlParameter("@ProductName", txtProductName));
            cmd.Parameters.Add(new SqlParameter("@Price", txtPrice));
            cmd.Parameters.Add(new SqlParameter("@SelfPrice", txtSelfPrice));
            cmd.Parameters.Add(new SqlParameter("@PriceWithOutAWD", PriceWithOutAWD));
            cmd.Parameters.Add(new SqlParameter("@UnitsInStock", NumericUpDown1));
            cmd.Parameters.Add(new SqlParameter("@Comment", txtComment));
            cmd.Parameters.Add(new SqlParameter("@bc", txtBarCode));
            cmd.Parameters.Add(new SqlParameter("@an", txtArtNumber));
            try
            {
                con.Open();
                cmd.ExecuteNonQuery();
            }
            finally
            {
                con.Close();
            }
        }