string cnnstr = ConfigurationManager.ConnectionStrings["library"].ToString();
            using (SqlConnection cnn = new SqlConnection(cnnstr))
                {
                cnn.Open();
                int idart = Convert.ToInt32(this.hdCod.Value.ToString());
                string querystring = "UPDATE Aree Set [Categoria] = @Categoria  WHERE ID = " + idart;
                SqlCommand esegui = new SqlCommand(querystring, cnn);
                esegui.Parameters.Add("@Categoria", SqlDbType.NVarChar, 255, "[Categoria]").Value = this.txtArea.Text;
                esegui.ExecuteNonQuery();
                cnn.Close();
                Response.Redirect("~/artico_gruppi_lista.aspx");
                }