DialogResult dlg;
fpSpread1.ActiveSheet.SetValue(0, 0, 20);
fpSpread1.ActiveSheet.SetValue(0, 1, 10);
fpSpread1.ActiveSheet.SetFormula(3, 0, "SUM(A1,B1)");
dlg = MessageBox.Show("Do you want to recalculate the formula?", "Recalculate", MessageBoxButtons.YesNo);
if (dlg == DialogResult.Yes)
{
fpSpread1.ActiveSheet.SetValue(0, 1, 100);
fpSpread1.ActiveSheet.Recalculate();
}