procedure TForm1.Button1Click(Sender: TObject);
var
 RetCode: Integer;
begin
 if CauseInvalid.Checked then
  RetCode := MessageBox(10,'Test','Invalid Message Box',mb_OK)
 else
  RetCode := MessageBox(0,'Test','Valid Message Box',mb_OK);

 RetValue.Text := IntToStr(RetCode);
end;