Calculate Days Between Two Dates - delphi

Question

Please help me find days between two dates.
I have two objects TDBDateEdit date1 and date2.
procedure Torder_form.date2Click(Sender: TObject);
var d3: TDateTime;
begin
d3:=date2.date - date1.date;
showmessage(datetostr(d3));
end.
I put to date1 = 07.10.2015
to date2 - 15.11.2015
Result must be: 39
But program gives me result: 07.02.1900
I found DaysBetween function. and I changed my codes like that
procedure Torder_form.date2Click(Sender: TObject);
var d3: TDateTime;
begin
d3:=DaysBetween(date2.date,date1.date);
showmessage(datetostr(d3));
end.
But programs says Result: 07.02.1900

Answer 1

You're trying to store a non-date value (the number of days between two dates) in a TDateTime value. Since you don't want a date, use a double instead, and interpret it as a double:
var
DaysDiff: Double;
begin
DaysDiff := Date2.Date - Date1.Date;
ShowMessage(FloatToStr(DaysDiff));
end;
Better yet, use the functions in DateUtils to do the work for you. If you need just whole days, use DaysBetween:
var
DaysDiff: Integer;
begin
DaysDiff := DaysBetween(Date2.Date, Date1.Date);
ShowMessage(IntToStr(DaysDiff));
end;
If you need fractional (partial) days, use DaySpan:
var
DaysDiff: Double;
begin
DaysDiff := DaySpan(Date2.Date, Date1.Date);
ShowMessage(FloatToStr(DaysDiff));
end;

Answer 2

I had the same problem in one of my projects. but after a little search in Delphi help, I find out Delphi has a rich set of functions on dates. Anyway you can use from 'DaysBetween' function to solve your problem. My code was something like this:
procedure TForm1.btnResultClick(Sender: TObject);
var
FirstDate, SecondDate: TDateTime;
format:TFormatSettings;
intDays: Integer;
begin
format:= TFormatSettings.Create();
format.ShortDateFormat := 'yyyy/mm/dd';
FirstDate := StrToDate(eFirstDate.Text,format);
SecondDate := StrToDate(eSecondDate.Text,format);
intDays:= DaysBetween(FirstDate,SecondDate);
eFinalDate.Text:= intToStr(intDays);
end;