获取本月第一天和最后一天的最简单的写法

var
  FirstDay, LastDay: TDateTime;
begin
  FirstDay := StrToDate(FormatDateTime('yyyy-MM-01', Now));
  LastDay := IncMonth(FirstDay) - 1;
  ShowMessage(FormatDateTime('yyyy-MM-01', Now)); //本月第一天
  ShowMessage(FormatDateTime('yyyy-mm-dd',IncMonth(FirstDay) - 1)); //本月最后一天
end;