//-------------------------------------------------------------------
//	xmas.cpp
//
//	This program shows which day-of-the-week is Christmas for a
//	specified year which is entered as a command-line argument.
//
//	programmer: ALLAN CRUSE
//	date begun: 28 SEP 2003
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), perror() 
#include <stdlib.h>	// for atoi(), exit() 
#include <string.h>	// for strncpy()

char daylst[] = "TueWedThuFriSatSunMon";

int main( int argc, char **argv )
{
	// get the command-line argument
	int	param = ( argc > 1 ) ? atoi( argv[1] ) : 2003;

	// check for invalid year
	if ( param < 1900 ) 
		{
		printf( "year cannot be before 1900\n" );
		exit(1);
		}

	// compute years since 1900
	int	years = param - 1900;

	// compute leap-years since 1900
	int	leaps = years / 4;
	
	// compute days since Christmas 1900
	int	days = 365*years + leaps;

	// compute the day-of-the-week	
	int	theday = days % 7;
	
	// report the day on which Christmas falls	
	char	report[] = "xxx, Dec 25\n";
	strncpy( report, &daylst[ 3*theday ], 3 ); 
	printf( report );
}