万年历（C语言版）

#include <stdio.h>
//判断输入的年份是否是闰年
int IsLeap(int  year)
{
	if((year%400==0) || ((year%4==0)&&(year%100!=0)))
		return 1;
	else
		return 0;
}
int Day[12]={31,28,31,30,31,30,31,31,30,31,30,31};
//计算一个月的最大天数(上一个月）
int Max_day(int year,int month)
{
    if(IsLeap(year)==1)
        Day[1]=29;
    return Day[month-1];
}
//计算输入的日期是这一年的第几天
int Total_day(int year,int month,int day)
{
	int sum = 0;
	for(int i=1;i<month;i++)
		sum+=Max_day(year,i);
	sum+=day;
	return sum;
}
//由输入的日期判断当天是星期几
int Weekday(int year,int month,int day)
{
	if(month==1||month==2)
	{
		month+=12;
		year--;
	}
	int week = (day+2*month+3*(month+1)/5+year+year/4-year/100+year/400)%7;
	return week;
}
void Display_week(int year,int month,int day)
{
	int weekday = Weekday(year,month,day);
	switch(weekday)
	{
		case 0:printf("%d年%d月%d日是星期一\n",year,month,day);break;
		case 1:printf("%d年%d月%d日是星期二\n",year,month,day);break;
		case 2:printf("%d年%d月%d日是星期三\n",year,month,day);break;
		case 3:printf("%d年%d月%d日是星期四\n",year,month,day);break;
		case 4:printf("%d年%d月%d日是星期五\n",year,month,day);break;
		case 5:printf("%d年%d月%d日是星期六\n",year,month,day);break;
		case 6:printf("%d年%d月%d日是星期日\n",year,month,day);break;
	}
}
//显示当月日历
void ShowCalendar(int year,int month,int day)
{
	int i;
	printf("==================================================\n");
	printf("日	一	二	三	四	五	六\n");
	printf("==================================================\n");
	int week = Weekday(year,month,1);	//由每月1号确定打印制表符的个数
	//printf("week:%d",week);
	for(i=0;i<=week;i++)
		printf("\t");
	int max = Max_day(year,month);
	for(int j=1;j<=max;j++)
	{
		if(i%7==0)
			printf("\n");

		printf("%d\t",j);
		i++;	

	}
	printf("\n==================================================\n");

}
int main()
{
	int year,month,day;
	printf("欢迎使用万年日历v1.0！\n");
	printf("请依次输入年，月，日：");
	scanf("%d%d%d",&year,&month,&day);
	Display_week(year,month,day);
	printf("%d年%d月%d日是这一年中的第%d天\n",year,month,day,Total_day(year,month,day));
	ShowCalendar(year,month,day);
	return 0;
}