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From: authorplaceholder@tiger.UUCP.UUCP
Newsgroups: comp.unix.wizards
Subject: Re: Date conversion question
Message-ID: <142700001@tiger.UUCP>
Date: Tue, 10-Mar-87 11:37:00 EST
Article-I.D.: tiger.142700001
Posted: Tue Mar 10 11:37:00 1987
Date-Received: Fri, 13-Mar-87 06:19:17 EST
References: <222@devon.UUCP>
Lines: 45
Nf-ID: #R:devon.UUCP:-22200:tiger.UUCP:142700001:000:900
Nf-From: tiger.UUCP!dic    Mar 10 10:37:00 1987



	I pulled this off of the net a few years ago so here it is
	again. No flames about this belonging in net.sources.

	
/* 
 * test as 
 * zeller month day year
 * year in 1987 form
 */
main(argc,argv)
int	argc;
char 	*argv[];
{
	char *zeller();
	char *day;

	day = zeller(atoi(argv[1]), atoi(argv[2]), atoi(argv[3]));
	printf("Day = %s\n",day);
	exit(0);
}
 
/****************************************************************
Compute day of week given any date. Year passed as e.g. 1984.
Algorithm by Zeller.
****************************************************************/
char *
zeller (m,d,y)
int m,d,y; {
 
static char *day_wk[] =
 { "Sun","Mon","Tue","Wed","Thu","Fri","Sat" };
int y0, y1, y2, m1;
int dbuf;
 
m1 = ((m+9) % 12) + 1;
y0 = (m <= 2)?(y-1):y;
y1 = y0 / 100;
y2 = y0 % 100;
 
dbuf = ( (26*m1-2)/10 + d + y2 + y2/4 + y1/4 - 2*y1 ) % 7;
if (dbuf < 0) dbuf += 7;
return day_wk[dbuf];
}