Category : Files from Magazines
Archive   : V12N09.ZIP
Filename : DOWGJ2.C

/***********************************************************************
DOWGJ2 - Day_Of_the_Week Gregorian or Julian calendar
************************************************************************

Author: Roberto R. Viscogliosi
Date Written : 10/92
Release: 1.1a

Modified by Douglas Boling

Program's Purpose:
This program computes the Day_Of_the_Week for a given date
using the Gregorian calendar as default, or the Julian calendar
when an extra argument is given at the command line.

Input Arguments:
mm dd yyyy [c]
where:
mm = month
dd = day
yyyy = year
[c] = any value forces the use of the Julian calendar;
no value uses the Gregorian calendar.

Example:
The input, "DOWGJ2 10 12 1492 j" shows that Columbus discovered
the New World on a Friday (Julian calendar).

Returns:
0 OK
1 Invalid calling syntax/Invalid Input Data

Last change: 14 Jan 93 2:34 pm
***********************************************************************/

#include
#include

#define OK 0
#define GRG 1

long dow (int, int, int, int);
void help (char *);

//====================================================================
// MAIN process
//====================================================================
int main (ac, av)
int ac;
char *av[];
{
int day, month, year, calendar = GRG, ret = OK;

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

for (;;) {
// check arguments passed
if (ac < 4) { // not enough args.
ret = !OK;
break;
}
// get/verify the input values
if (((month = atoi (av[1])) < 1) ||
((day = atoi (av[2])) < 1) ||
((year = atoi (av[3])) < 1)
) { // invalid values
ret = !OK;
break;
}
// check if Julian calendar requested
if (ac > 4) { // reset the calendar indicator
calendar = !GRG;
}
// prevent overflow by check year size
if (year > 9999) { // year too large
ret = !OK;
break;
}
// compute and show the day_of_the_week
printf ("%02d/%02d/%04d is on %s %s\n",
month, day, year,
dowstr [dow (month, day, year, calendar)],
(calendar == GRG) ? "" : "(Julian calendar)"
);
break;
}
// check for errors
if (ret) {
help (av[0]);
}
exit (ret);
}

//======================================================================
// DOW - Return the day of the week value 0-6 (0 = Sunday)
// based on the date (month, day, year) and calendar
//======================================================================
long dow (month, day, year, calendar)
int month, day, year, calendar;
{
static char month_val[12] = {
// J F M A M J J A S O N D
6,2,2,5,0,3,5,1,4,6,2,4
};
long DayOfWeek;

DayOfWeek = day + month_val[month - 1];

if (month < 3) {
if (calendar == GRG) {
if (!(year % 4) && (year % 100) || !(year % 400))
DayOfWeek--;
} else
if (!year %4)
DayOfWeek--;
}

DayOfWeek += year + (year / 4);
if (calendar == GRG)
DayOfWeek += (year / 400) - (year / 100);
else
DayOfWeek += 5;

DayOfWeek %= 7;
return DayOfWeek;
}

//====================================================================
// HELP - Print the help info
//====================================================================
void help (fn)
char *fn;
{
printf ("\nWelcome to DOWGJ2 (DOW Gregorian or Julian) Version 1.1\n");
printf (" by R. Viscogliosi\n");
printf (" modified by Douglas Boling\n");

printf ("\nTo use it, please enter:\n");
printf ("\n %s mm dd yyyy [c]\n", fn);
printf ("\n (If [c] is specified then the date is in Julian,\n");
printf (" else the date defaults to the Gregorian calendar)\n");
printf ("\n (e.g. 'DOWGJ2 10 12 1492 j' was on Friday (Julian))\n");
}