week.c

星期算法,即知道日期,即可知道该天是星期几

#include <stdio.h>
#define uchar unsigned char
#define uint unsigned int
uchar week(uint year,uchar month,uchar day);
void main(void)
{
	uchar a;
	uchar month,day;
	uint year;
    year=1997;month=7;day=1;
		while(1)
		{
   a=week(year,month,day);
     }
}

uchar week(uint year,uchar month,uchar day)
{
	uchar centry,return_week;
	centry=year/100;
	year=year%100;
	if(month>=3&month<=12) 
	   month=month-2;
	else
	   {
	      month=month+12-2;
		  year=year-1;
		}
	return_week=( day+(13*month-1)/5+year+centry/4+year/4-2*centry )%7;
	return return_week;
}