根据日期计算星期几

// 根据日期计算星期几
static int CaculateWeekDay(int year, int month, int day)
{
	int weekday;
	
	// 一月和二月被当作前一年的
	if ((month == 1) || (month == 2))
	{
		month += 12;
		year--;
	}
	
	weekday = (day + 2 * month + 3 * (month + 1) / 5 + year + year / 4 - year / 100 + year / 400) % 7 + 1;
	if (weekday == 7) weekday = 0;
	return weekday;
}