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From: devine@vianet.UUCP (Bob Devine)
Newsgroups: net.lang.c
Subject: Re: Calendar Functions (simpler leap year calculation)
Message-ID: <34@vianet.UUCP>
Date: Fri, 12-Sep-86 16:33:30 EDT
Article-I.D.: vianet.34
Posted: Fri Sep 12 16:33:30 1986
Date-Received: Sun, 14-Sep-86 03:48:28 EDT
References: <206@cascade.STANFORD.EDU> <1229@loral.UUCP>
Distribution: net.lang.c
Organization: ViaNetix, Inc., Boulder, CO
Lines: 28

Dave Lewis writes:
> leapyear (year)
> int year;
> {
>   if (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0))
>      return (1);
>   else
>      return (0);
> }

  While this works, it is overkill.  Unless you believe that your
code will make it to the year 2100, a simple test for divisibility
by 4 is sufficient.  If you really want an algorithm for all years,
you then need to also test for years divisible by 4000...

int
leapyear(year)
    int year;
{
    /* works for the years 1901-2099 */
    return(year%4);
}

Or if you want a simple cpp macro:

#define  isleapyear(year)   ((year)%4)

Bob Devine