I have a problem in datagridview code, any solution

DataTable dt = blord.getitembyitem_id(Convert.ToInt32(lblitem_id.Text));
           if (dt.Rows.Count > 0)
           {
               if (dataGridView1.Rows[i].Cells[0].Value.ToString() == "")
               {
                   dataGridView1.Rows.Add();
                   dataGridView1.Rows[i].Cells[0].Value = dt.Rows[0]["item_name"].ToString();
                   dataGridView1.Rows[i].Cells[1].Value = quantity;
                   dataGridView1.Rows[i].Cells[2].Value = dt.Rows[0]["item_price"].ToString();
                   i++;
               }
               else
               {
                   dataGridView1.Rows[i].Cells[1].Value = dataGridView1.Rows[i].Cells[1].Value + 1.ToString();
               }
           }