Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!batcomputer!rpi!pawl4.pawl.rpi.edu!mketch
From: mketch@pawl.rpi.edu (Michael D. Ketchen)
Newsgroups: comp.lang.pascal
Subject: Re: Day-of-week algorithm, please!
Summary: It's the latter...
Keywords: day of the week
Message-ID: <1265@rpi.edu>
Date: 13 Apr 89 18:14:58 GMT
References: <19040@adm.BRL.MIL> <1780001@hpcc01.HP.COM> <2394@maccs.McMaster.CA>
Sender: usenet@rpi.edu
Organization: Rensselaer Polytechnic Institute, Troy, NY
Lines: 37

In article <2394@maccs.McMaster.CA> cs3b3aj@maccs.UUCP (Stephen M. Dunn) writes:
>In article <1780001@hpcc01.HP.COM> azarian@hpcc01.HP.COM (Randy Azarian) writes:
>...
>>  total := total + + (year - 1) div 4;
>
>   But watch out, because not every year such that year mod 4 = 0 is a leap
>year!  The strangeness in the pattern occurs on century years, but I'm not 
>sure which way round it is.  It is either that years divisible by 400 are
>_not_ leap years, or that any century year is not a leap year _except_
>for years divisible by 400.
>      (etc. etc.)
>   Does anyone know which way it is? ...
>! Stephen M. Dunn, cs3b3aj@maccs.McMaster.CA

Every fourth year is a leap year (1988, 1992, etc.), unless it falls on the
end of a century (1800, 1900, etc), in which case it's not a leap year,
_unless_ it's a multiple of 400 (2000, 2400, etc.), in which case it _is_
a leap year.  Confusing, eh?  The following function should return TRUE if
the year passed is leap.

function IsALeap (year: integer): boolean;
(* returns TRUE if 'year' is a leap year *)
begin
  IsALeap:=FALSE;
  if ((year mod 4)=0) and ((year mod 100)<>0)
     or ((year mod 400)=0) then
    IsALeap:=TRUE
end;  (* IsALeap *)

Hope this helps...

- Mike

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