Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!haven!adm!xadmx!RDK%vm.temple.edu@cunyvm.cuny.edu
From: RDK%vm.temple.edu@cunyvm.cuny.edu (Robert Keiser)
Newsgroups: comp.lang.pascal
Subject: Re: Day-of-week algorithm, please!
Message-ID: <19065@adm.BRL.MIL>
Date: 10 Apr 89 18:35:30 GMT
Sender: news@adm.BRL.MIL
Lines: 28

I have used the following algorithm to get the Day of week.  It will work for
any date after 1800.  In the following, Year is a 4 digit integer i.e. 1989
not just the 89 part.


(*     N = 1461*f(year,month) / 4 + 153*g(month) / 5 + day               *)
(*                                                                       *)
(* where:                                                                *)
(*          f(year,month) = year - 1         if month <= 2               *)
(*                          year             otherwise                   *)
(*                                                                       *)
(*          g(month)      = month + 13       if month <= 2               *)
(*                          month + 1        otherwise                   *)
(*                                                                       *)
(* Then apply the following formula to N                                 *)
(*     dow = (N - 621,049) MOD 7                                         *)
(*                                                                       *)
(* This formula was found in _Programming in ANSI C_                     *)
(* by Stephen G. Kochan pg. 188                                          *)

Robert Keiser
Systems Analyst
Temple University Computer Activities

Bitnet   : RDK@Templevm
Internet : RDK@vm.temple.edu
US Mail  : Temple University
           Philadelphia, PA 19122