Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!sdcsvax!nosc!humu!uhmanoa!uhccux!julian
From: julian@uhccux.UUCP (Julian Cowley)
Newsgroups: comp.sys.ibm.pc
Subject: Re: day of week
Message-ID: <1510@uhccux.UUCP>
Date: 2 Feb 88 11:19:39 GMT
References: <141900013@occrsh.ATT.COM> <3170@killer.UUCP>
Organization: U. of Hawaii, Manoa (Honolulu)
Lines: 35
Summary: another formula

Here is a formula that I picked out of an old HP-2000 calendar program.
Basically it figures out how many days there are since January 1, 1900.
As that date was a Monday, the result modulo 7 starts on that day of
the week.  This should work for all of the years in this century, with
the exception of 1900 because that year was not a leap year.

Sample C program:

char *daystr[7] = {
  "Monday",
  "Tuesday",
  "Wednesday",
  "Thursday",
  "Friday",
  "Saturday",
  "Sunday" };

main()
{
  int day, year, month, date;

  puts("Enter the date as mm/dd/yy");
  scanf("%d/%d/%d", &month, &date, &year);

  day = ((year-1)*365 + (year-1)/4 + (int) ((month-1)*30.57+0.5) -
        (1+(year%4 != 0))*(month > 2) + date) % 7;

  printf("That day was a %s\n", daystr[day]);
}

Cheers.

 //////  /////  Julian Cowley, University of Hawaii  | "It's not the size of
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