日期计算

#include<stdio.h>
#include<iostream>
using namespace std;
//日期函数

int days[12]={31,28,31,30,31,30,31,31,30,31,30,31};
struct date{
	int year,month,day;
};

//判闰年
inline int leap(int year){
	return (year%4==0&&year%100!=0)||year%400==0;
}

//判合法性
inline int legal(date a){
	if (a.month<0||a.month>12)
		return 0;
	if (a.month==2)
		return a.day>0&&a.day<=28+leap(a.year);
	return a.day>0&&a.day<=days[a.month-1];
}

//比较日期大小
inline int datecmp(date a,date b){
   if (a.year!=b.year)
	   return a.year-b.year;
   if (a.month!=b.month)
	   return a.month-b.month;
   return a.day-b.day;
}

//返回指定日期是星期几
int weekday(date a){
	int tm=a.month>=3?(a.month-2):(a.month+10);
	int ty=a.month>=3?a.year:(a.year-1);
	return (ty+ty/4-ty/100+ty/400+(int)(2.6*tm-0.2)+a.day)%7;
}

//日期转天数偏移
int date2int(date a){
	int ret=a.year*365+(a.year-1)/4-(a.year-1)/100+(a.year-1)/400,i;
	days[1]+=leap(a.year);
	for (i=0;i<a.month-1;ret+=days[i++]);
	days[1]=28;
	return ret+a.day;
}

//天数偏移转日期
date int2date(int a){
	date ret;
	ret.year=a/146097*400;
	for (a%=146097;a>=365+leap(ret.year);a-=365+leap(ret.year),ret.year++);
	days[1]+=leap(ret.year);
	for (ret.month=1;a>=days[ret.month-1];a-=days[ret.month-1],ret.month++);
	days[1]=28;
	ret.day=a+1;
	return ret;
}

int main()
{
    date a,b;
    a.year=2014,a.month=8,a.day=28;
    b.year=2014,b.month=8,b.day=29;
    //计算日期之间相差多少天
    int t1=date2int(a);//a的天数
    int t2=date2int(b);//b的天数
    printf("%d\n",t2-t1);
    //计算当前日期过了day天的日期
    int day=1;
    date c=int2date(day+t1);
    printf("%d %d %d",c.year,c.month,c.day);
    return 0;
}