计算从出生到现在活了多少天

C语言写的，switch计算部分采用了一本狂人C书的类似写法，感觉很有创意。

#include <stdio.h>


typedef struct
{
    int year;
    int month;
    int day;
}Date;

int date_minus(Date *now,Date *birth);
int numOfYear(Date *date);
int isLeapYear(int year);

int main(void)
{
    Date birth={1993,4,4};
    Date now={2013,9,17};
    printf("%d
",date_minus(&now,&birth));
    return 0;
}

int date_minus(Date *now,Date *birth)
{
    
    int days;
    int year;

    if(now->year==birth->year)    //同一年的情况
        return numOfYear(now)-numOfYear(birth)+1;
    else if(now->year<birth->year)
        return -1;

    //出生年的后几天
    days=(isLeapYear(birth->year)?366:365)-numOfYear(birth)+1;

    //中间年
    for(year=birth->year+1;year < now->year;year++)
        days+=isLeapYear(year)?366:365;

    //今年的前几天
    return days+numOfYear(now);
}

//一年中的第几天
int numOfYear(Date *date)
{
    int days=date->day;
    switch(date->month-1)
    {
    case 11:days+=30;
    case 10:days+=31;
    case 9:days+=30;
    case 8:days+=31;
    case 7:days+=31;
    case 6:days+=30;
    case 5:days+=31;
    case 4:days+=30;
    case 3:days+=31;
    case 2:days+=isLeapYear(date->year) ? 29 :28;
    case 1:days+=31;
        return days;
    }
    return -1;
}

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