Insert Query problem

Question

Hi 

I have written query for inserting records in SQL daatbase from datagridview & some comboboxes & textboxes.

But it is given error like null expection was unhandled.

 

Please help to detect what is wrong in below code.

 

private void btnsubmit_Click(object sender, EventArgs e)

{

for (int i = 0; i < cnt; i++)

{

String str = "INSERT INTO JOB_Quality_Rating values('" + comboBox1.SelectedItem + "','" + comboBox3.SelectedItem + "','" + textBox1.Text + "','" + cmbtaskno.SelectedItem + "','" + comboBox2.SelectedItem + "','" + dataGridView1.Rows[i].Cells[0].Value.ToString() + "','" + dataGridView1.Rows[i].Cells[1].Value.ToString() + "','" + dataGridView1.Rows[i].Cells[2].Value.ToString() + "','" + txtTotal.Text + "','" + mdlconnection.user_id + "','" + DateTime.Now + "')";

//int d = mdlconnection.excuteQuery(str);

//if (d > 0)

mdlconnection.excuteQuery(str);

{

MessageBox.Show("Job Quality Save sucessfully");

}

}

}