一个日期是星期几

#include <stdio.h>
#include <stdlib.h>

/*
	输入一个日期，输出该日期是星期几。
*/

int monthDays[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

int getWeekDay(int year, int month, int day);
int isGoodYear(int year);
int isGoodMonth(int month);
int isGoodDay(int year, int month, int day);
int isLeapYear(int year);
int dayOfYear(int year, int month, int day);
int daysBetweenYear(int year1, int year2);
int daysBetweenDays(int year1, int month1, int day1, int year2, int month2, int day2);

int main(){
	int year, month, day;
	while (fflush(stdin), scanf("%d%d%d", &year, &month, &day) != EOF){
		if (isGoodYear(year) && isGoodMonth(month) && isGoodDay(year, month, day))	//判断输入是否合法
			printf("%d\n", getWeekDay(year,month,day));
		else
			printf("Please input a right date.\n");
	}
	system("pause");
	return 0;
}

int getWeekDay(int year, int month, int day){
	//基准取2016/1/3，周日
	//SUN返回0
	//MON-SAT分别返回1-6
	if ((year >= 2016) && (month >= 1) && (day >= 3))
		return daysBetweenDays(2016, 1, 3, year, month, day) % 7;
	else
		return (7 - daysBetweenDays(year, month, day, 2016, 1, 3) % 7) % 7;
}

int daysBetweenDays(int year1, int month1, int day1, int year2, int month2, int day2){
	//日期1<日期二为负数
	//日期1>日期二为正数
	int days1 = dayOfYear(year1, month1, day1);
	int days2 = dayOfYear(year2, month2, day2);
	int days3 = daysBetweenYear(year1, year2);
	int totalDays = days2 + days3 - days1;
	return totalDays;
}

int daysBetweenYear(int year1, int year2){
	//year1 < year2为正数
	//year1 > year2为负数
	int maxYear = (year1 > year2) ? year1 : year2;
	int minYear = (year1 > year2) ? year2 : year1;
	int totalDays = 0;
	for (int i = minYear; i < maxYear; ++i)
		if (isLeapYear(i))
			totalDays += 366;
		else
			totalDays += 365;
	if (minYear == year1)
		return totalDays;
	else
		return -totalDays;
}

int dayOfYear(int year, int month, int day){//当年第几天
	int total = 0;
	for (int i = 0; i < month - 1; ++i)
		total += monthDays[i];
	total += day;
	if (isLeapYear(year) && (month > 2))
		total++;
	return total;
}

int isLeapYear(int year){
	if (((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0))
		return 1;
	else
		return 0;
}

int isGoodYear(int year){
	if (year >= 1900)
		return 1;
	else
		return 0;
}

int isGoodMonth(int month){
	if ((month >= 1) && (month <= 12))
		return 1;
	else
		return 0;
}

int isGoodDay(int year, int month, int day){
	switch (month)
	{
	case 2:
		if (isLeapYear(year))
			if ((day >= 1) && (day <= 29))
				return 1;
			else if ((day >= 1) && (day <= 28))
				return 1;
			else
				return 0;
	case 4:
	case 6:
	case 9:
	case 11:
		if ((day >= 1) && (day <= 30))
			return 1;
		else
			return 0;
	case 1:
	case 3:
	case 5:
	case 7:
	case 8:
	case 10:
	case 12:
		if ((day >= 1) && (day <= 31))
			return 1;
		else
			return 0;
	default:
		printf("month error in day judge.\n");
		return 0;
	}
}