以下是一个完整的关于日期运算的程序，从中你会得到很好的解答：
#include 
#pragma hdrstop
#include "Unit1。h"
//-------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*。
  dfm"
TForm1 *Form1;
//-------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
        : TForm(Owner)
{
}
//-------------------------------------------------------
void __fastcall TForm1::N3Click(TObject *Sender)
{
  //显示当前日期
  if(RichEdit1->Visible==false)
    RichEdit1->Visible=true;
  RichEdit1->Clear();
  TDateTime Date(Now());
  AnsiString S;
  S=Date。
  FormatString("yyyymmdd");
  S+="\n"+Date。FormatString("yyyy mm dd");
  S+="\n"+Date。FormatString("yyyy-mm-dd");
  S+="\n"+Date。
  FormatString("yyyy mm dd  dddd");
  S+="\n"+Date。FormatString("dddddd");
  RichEdit1->Text=S;
}
//-------------------------------------------------------
void __fastcall TForm1::N4Click(TObject *Sender)
{
  //显示当前时间
  if(RichEdit1->Visible==false)
    RichEdit1->Visible=true;
  RichEdit1->Clear();
  String S;
  S=FormatDateTime("hhnnss", Now())+"\n";
  S=FormatDateTime("hh:nn:ss", Now())+"\n";
  TDateTime Time(Now());
  RichEdit1->Text=S+Time。
  FormatString("h:nn:ss am/PM");
}
//-------------------------------------------------------
void __fastcall TForm1::N6Click(TObject *Sender)
{
  if(RichEdit1->Visible==false)
    RichEdit1->Visible=true;
  RichEdit1->Clear();
  TDateTime Date(Now());
  RichEdit1->Lines->Add(Date。
  DateTimeString());
  RichEdit1->Lines->Add("当前时间："+FormatDateTime("dddddd dddd", Now())+"　"+FormatDateTime("hh:nn:ss", Now()));
}
//-------------------------------------------------------
void __fastcall TForm1::N7Click(TObject *Sender)
{
  if(RichEdit1->Visible==false)
    RichEdit1->Visible=true;
  RichEdit1->Clear();
  TDate Date1(Now());
  String Date2="2002-10-01";
  int Date_num=int(Date1-StrToDate(Date2));
  RichEdit1->Lines->Add("日期相差"+IntToStr(Date_num)+"天");
}
//-------------------------------------------------------
void __fastcall TForm1::N8Click(TObject *Sender)
{
  RichEdit1->Lines->Add("当前时间："+FormatDateTime("hh:nn:ss", Now()));
  unsigned long CurTime;
  unsigned long DelayTime;
  // 设置时间为2秒
  DelayTime=5000;
  CurTime=GetTickCount();
  unsigned long Inter;
  do
  {
    Inter=GetTickCount()-CurTime;
  } while(InterVisible==false)
    RichEdit1->Visible=true;
  RichEdit1->Clear();
  RichEdit1->Lines->Add("现在时间："+FormatDateTime("hh:nn:ss", Now()));
  RichEdit1->Lines->Add("时间相差"+IntToStr(GetTickCount()-CurTime)/1000+"秒");
}
//-------------------------------------------------------
void __fastcall TForm1::N10Click(TObject *Sender)
{
  if(RichEdit1->Visible==false)
    RichEdit1->Visible=true;
  RichEdit1->Clear();
  TTime One(Now());
  One++;
  TTime Two(Now());
  if(One>Two)
    RichEdit1->Lines->Add(One。
  TimeString()+">"+Two。TimeString());
  if(One==Two)
    RichEdit1->Lines->Add(One。TimeString()+"="+Two。TimeString());
  if(OneLines->Add(One。
  TimeString()+"Visible==false)
    RichEdit1->Visible=true;
  RichEdit1->Clear();
  TDateTime date1(Now());
  String date2="02-12-10 16:27:00";
  TDateTime temp=StrToDateTime(date2);
  double aa=date1-temp;
  RichEdit1->Lines->Add("当前时间："+date1。
  TimeString());
  RichEdit1->Lines->Add("相隔时间"+IntToStr(int(aa/1。15740695036948E-5))+"秒");
}
。