DataTable dt0 = new DataTable();
dt0.Columns.Add(new DataColumn("check", typeof(bool)));
dt0.Columns.Add(new DataColumn("value", typeof(int)));
for (int i =  0 ; i <  10 ; i++)
{
    DataRow r = dt0.NewRow();
    r["check"] = i %  2  ==  0 ;
    r["value"] = i +  1 ;
    dt0.Rows.Add(r);
}

DataGridView dgv0 = new DataGridView();
dgv0.DataSource = dt0;
dgv0.Dock = DockStyle.Top;

Label lbl0 = new Label();
lbl0.Text = "";
lbl0.Left =  10 ;
lbl0.Top =  250 ;

Button btn0 = new Button();
btn0.Text = "Press me";
btn0.Left =  10 ;
btn0.Top =  220 ;
btn0.Click += delegate 
{
    int val =  0 ;
    foreach (DataRow row in dt0.Rows)
    {
        if (bool.Parse(row["check"].ToString()) == true)
        {
            val += int.Parse(row["value"].ToString());
        }
    }
    lbl0.Text = val.ToString();
};
this.Controls.AddRange(new Control[] { dgv0, btn0, lbl0 });

DataTable dt0 = new DataTable();
dt0.Columns.Add(new DataColumn("check", typeof(bool)));
dt0.Columns.Add(new DataColumn("value", typeof(int)));
for (int i =  0 ; i <  10 ; i++)
{
    DataRow r = dt0.NewRow();
    r["check"] = i %  2  ==  0 ;
    r["value"] = i +  1 ;
    dt0.Rows.Add(r);
}

BindingSource bs0 = new BindingSource();
bs0.DataSource = dt0;

DataGridView dgv0 = new DataGridView();
dgv0.DataSource = bs0;
dgv0.Dock = DockStyle.Top;

Label lbl0 = new Label();
lbl0.Text = "";
lbl0.Left =  10 ;
lbl0.Top =  250 ;

dgv0.CellValueChanged += delegate(object exSender, DataGridViewCellEventArgs exE)
{
    int val = lbl0.Text.Trim() != string.Empty ? int.Parse(lbl0.Text.Trim()) :  0 ;
    if (bool.Parse(dgv0.Rows[exE.RowIndex].Cells[exE.ColumnIndex].Value.ToString()) == true)
    {
        val += int.Parse(dt0.Rows[bs0.Position]["value"].ToString());
    }
    else
    {
        val -= int.Parse(dt0.Rows[bs0.Position]["value"].ToString());
    }

    lbl0.Text = val.ToString();
};

this.Controls.AddRange(new Control[] { dgv0, lbl0 });