Re: Calculate week number of given date

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From: Boris Nienke (nospam_at_nsonic.de)
Date: 02/24/04 

Date: Tue, 24 Feb 2004 14:59:13 +0100

Some Delphi-Procedures... don't know - but some things may be easier with
C# :

function dateWeekOfYear(D: TDateTime): Integer; { Armin Hanisch }
const
  t1: array[1..7] of ShortInt = ( -1, 0, 1, 2, 3, -3, -2);
  t2: array[1..7] of ShortInt = ( -4, 2, 1, 0, -1, -2, -3);
var
  doy1,
  doy2 : Integer;
  NewYear : TDateTime;
begin
  NewYear:=dateBeginOfYear(D);
  doy1 := dateDayofYear(D) + t1[DayOfWeek(NewYear)];
  doy2 := dateDayofYear(D) + t2[DayOfWeek(D)];
  if doy1 <= 0 then
    Result := dateWeekOfYear(NewYear-1)
  else if (doy2 >= dateDayofYear(dateEndOfYear(NewYear))) then
    Result:= 1
  else
    Result:=(doy1-1) div 7+1;
end;

function dateBeginOfYear(D: TDateTime): TDateTime;
var
  Year,Month,Day : Word;
begin
  DecodeDate(D,Year,Month,Day);
  Result:=EncodeDate(Year,1,1);
end;

function dateDayOfYear(D: TDateTime): Integer;
begin
  Result:=Trunc(D-dateBeginOfYear(D))+1;
end;

Boris

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