Looping column data insert into SQL Server database

Question

I am new to C#. My problem is I want to insert the ean, description, bookcode, price and discount into SQL Server with the qty from column 7 and above:

My current code is able to insert the data but the quantity is already defined. I am thinking to do looping, but I got an error

Must declare the scalar variable

and I'm not sure my logic is correct.

Here's a screenshot of my SQL Server table:

My code:

private void button3_Click(object sender, EventArgs e)
{ 
    using (SqlConnection conn = new SqlConnection(";Trusted_Connection=False"))
    using (SqlCommand comm = new SqlCommand())
    { 
            comm.Connection = conn;
            conn.Open(); 

            for (int i = 1; i < dataGridView2.Rows.Count; i++)
            {
                comm.CommandText = "INSERT INTO SOLine (CustID,Bookcode,Barcode,Description,Price,Disc,Qty) VALUES ('2058 KBC',@bookcode,@barcode,@desc,@price,@disc,@qty)";

                SqlParameter bookcode = comm.Parameters.AddWithValue("@bookcode", dataGridView2.Rows[i].Cells["BOOKCODE"].Value);
                SqlParameter barcode = comm.Parameters.AddWithValue("@barcode", dataGridView2.Rows[i].Cells["3"].Value);
                SqlParameter desc = comm.Parameters.AddWithValue("@desc", dataGridView2.Rows[i].Cells["4"].Value);
                SqlParameter price = comm.Parameters.AddWithValue("@price", dataGridView2.Rows[i].Cells["5"].Value);
                SqlParameter disc = comm.Parameters.AddWithValue("@disc", dataGridView2.Rows[i].Cells["6"].Value);
                //SqlParameter qty = comm.Parameters.AddWithValue("@qty", dataGridView2.Rows[i].Cells["7"].Value);

                if (dataGridView2.Rows[i].Cells["BOOKCODE"].Value == null) 
                {
                    bookcode.Value = DBNull.Value; 
                }

                if (dataGridView2.Rows[i].Cells["3"].Value == null) 
                {
                    barcode.Value = DBNull.Value; 
                }

                if (dataGridView2.Rows[i].Cells["4"].Value == null)
                { 
                    desc.Value = DBNull.Value; 
                }

                if (dataGridView2.Rows[i].Cells["5"].Value == null) 
                {
                    price.Value = DBNull.Value; 
                }

                if (dataGridView2.Rows[i].Cells["6"].Value == null)
                { 
                    disc.Value = DBNull.Value; 
                }

                // if (dataGridView2.Rows[i].Cells["7"].Value == null) 
                // { 
                //       qty.Value = DBNull.Value; 
                // }

                for (int q = 7; q <= dataGridView2.Columns.Count; q++) //dataGridView2.Columns.Count
                {
                    int w = 1;
                    w++;
                    comm.Parameters.Add("@qty", SqlDbType.Int).Value = dataGridView2.Rows[w].Cells[q].Value;
                    comm.Parameters.Clear();
                }

                comm.ExecuteNonQuery();
                comm.Parameters.Clear();
            } 

            MessageBox.Show("Save SQL"); 

            //try
            //{ 
            //    comm.ExecuteNonQuery();
            //}
            //catch (Exception ex)
            //{
            //    MessageBox.Show(ex.ToString());
            //}
        } 
    }

Answer 1

In your for loop you have:

comm.Parameters.Add("@qty", SqlDbType.Int).Value = dataGridView2.Rows[w].Cells[q].Value;
comm.Parameters.Clear();

So you are clearing all of the parameters you've previously added before you execute the query.