Checkbox inside a Datagridview

    private void button1_Click(object sender, EventArgs e)
    {
        DataGridViewCell dc = null;
        DataGridViewCheckBoxCell cbx = null;
        double mySum = 0;
        string s = string.Empty;
        foreach (DataGridViewRow dr in dataGridView1.Rows)
        {
            dc = dr.Cells[2];
            cbx = (DataGridViewCheckBoxCell)dc;
            if (Convert.ToBoolean(cbx.Value))
            {
                mySum += double.Parse(dr.Cells[0].Value.ToString());
            }
        }
        s = String.Format("Total sum: {0}", mySum.ToString());
        MessageBox.Show(s);
    }
}