分解和组合日期

 uses SysUtils, DateUtils

【EncodeDate - 组合日期】
var
  iYear, iMonth: Integer;
  dFirstDate, dLastDate: TDateTime;
begin
  iYear := 2011;
  iMonth := 10;
  //指定月份的第1天
  dFirstDate := EncodeDate(iYear, iMonth, 1);

  //指定月份的最后1天
  dLastDate := EndOfTheMonth(dFirstDate);

  ...
end;

【EncodeDate - 拆分日期】
var
  iYear, iMonth, iDay: Word;
  dToday: TDateTime;
begin
  dToday := Date;
  DecodeData(dToDay, iYear, iMonth, iDay);
  ..
end;