计算自定义日期是16年1月1日的第几天第几周星期几

此函数的实现功能为计算自定义日期距离 2016年1月1日 的 天数 ，周数 ，星期 。

因为年份在定义的时候定义为 unsigned char 类型，所以有最大年份的限制，如果不想有限制，那么更改年份的定义就可以了。

//计算今天是今年的第几周星期几
//今天的日期自己定

#include<stdio.h>

//以下是计算的时间99年12月31日，这个时间可以改
#define SYSYEAR 99
#define SYSMONTH 12
#define SYSDAY 31

//结构体的定义部分
//系统时间
struct _SystemTime
{
	unsigned char month;     //系统月
	unsigned char day;       //系统天
	unsigned char week;      //系统星期
	unsigned char year;         //系统年
}SystemTime;

//判断是否是闰年
//返回1：是闰年
//返回0：不是闰年
char LeapYear()
{
	unsigned char sysyear;
	sysyear = SystemTime.year+2000;
/*
	 printf("=================判断是不是闰年===================\n");
	 printf("系统时间：\n");
	 printf("年:%d\n",SystemTime->year);
	 printf("月:%d\n",SystemTime->month);
	 printf("日:%d\n",SystemTime->day);
*/
	if ( ( (sysyear%100!=0) && (sysyear%4==0) ) || (sysyear%400==0) )
 	{
		//printf("今年是闰年\n");
		return 1;           //是闰年
 	}
 	else
 	{
		//printf("今年不是闰年\n");
		return 0;           //不是闰年
 	}
}

//判断今天是今年的第几天
int numberday()
{
	unsigned char i = 0;
	unsigned short number = 0;
	unsigned char monthnum[]={31,28,31,30,31,30,31,31,30,31,30,31};
 /*
	 printf("=============判断今天是今年的第几天===============\n");
	 printf("系统时间：\n");
	 printf("年:%d\n",SystemTime.year);
	 printf("月:%d\n",SystemTime.month);
	 printf("日:%d\n",SystemTime.day);
 */
	if(LeapYear()==1)
	{
		monthnum[1] = 29;
	}
	else
	{
		monthnum[1] = 28;
	}
	if(SystemTime.month != 1)
	{
		for(i;i<(SystemTime.month-1);i++)
		{
			 number = number + monthnum[i];
			//printf("整月天数%d\n",number);
		}
		number = number + SystemTime.day;
		printf("今年天数%d\n",number);
	}
	else
	{
		number = SystemTime.day;
		printf("今年天数%d\n",number);
	}
	return number;
}

//计算今天是今年的第几周
int countweek()
{
	//2016年1月1日星期5
	unsigned char year = 16;
	unsigned char month = 1;
	unsigned char day = 1;
	unsigned char week = 5;
	unsigned short yearstar;
	unsigned char yuncount = 0;
	unsigned char weeknumber = 0;
	unsigned short totalday = 0;
	unsigned short totalweek = 0;
 /*
	 printf("=============算今天是今年的第几周===============\n");
	 printf("系统时间：\n");
	 printf("年:%d\n",SystemTime->year);
	 printf("月:%d\n",SystemTime->month);
	 printf("日:%d\n",SystemTime->day);
 */
 /*
	yearcha = SystemTime.year - year;
	//printf("相差年数：%d\n",yearcha);
	yuncount = yearcha / 4 + 1;
	//printf("闰年个数：%d\n",yuncount);
 */
 	yearstar = 2000 + year;
	for(yearstar;yearstar<(SystemTime.year+2000);yearstar++)
	{
		if ( ( (yearstar%100!=0) && (yearstar%4==0) ) || (yearstar%400==0) )
		{
			yuncount++;
			//printf("闰年个数为：%d\n",yuncount);
		}
	}
	printf("闰年个数为：%d\n",yuncount);
	totalday = numberday();
	//printf("当年天数：%d\n",totalday);
 	totalday = totalday + (SystemTime.year - year) * 365 + yuncount;
 	printf("一共天数：%d\n",totalday);
 	totalday = totalday - 1;                		//比如第二天说明过了一天，所以需要处理
 	weeknumber = totalday % 7 + week;
 	weeknumber = weeknumber % 7;                	//0表示星期日
	//printf("星期余数：%d\n",weeknumber);
	if(weeknumber == 0)
	{
		weeknumber = 7;
	}
	printf("===============================\n");
	printf("\n");
	printf("星期%d\n",weeknumber);
	printf("\n");
	printf("===============================\n");
	if(weeknumber>=week)
	{
	 	return totalday/7+1;
	}
	else
	{
	 	return totalday/7+2;
	}
}
unsigned short function()
{
 	unsigned short weekcount;
 /*
	printf("系统时间：\n");
	printf("年:%d\n",SystemTime.year);
	printf("月:%d\n",SystemTime.month);
	printf("日:%d\n",SystemTime.day);
 */
	weekcount = countweek( &SystemTime );
	return weekcount;
}
int main()
{
	unsigned short weekcount;
	SystemTime.year = SYSYEAR;
	SystemTime.month = SYSMONTH;
	SystemTime.day = SYSDAY;
	weekcount = function();
	printf("\n\n");
	printf("===============================\n");
	printf("\n");
	printf("当前是第%d周\n",weekcount);
	printf("\n");
	printf("===============================\n");
	return 0;
}
//结果展示部分
/*
闰年个数为：21
今年天数365
一共天数：30681
===============================

星期4

===============================


===============================

当前是第4384周

===============================
*/