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。
 1 #include <stdio.h>
 2 
 3 
 4 typedef struct
 5 {
 6     int year;
 7     int month;
 8     int day;
 9 }Date;
10 
11 int date_minus(Date *now,Date *birth);
12 int numOfYear(Date *date);
13 int isLeapYear(int year);
14 
15 int main(void)
16 {
17     Date birth={1993,4,4};
18     Date now={2013,9,17};
19     printf("%d
",date_minus(&now,&birth));
20     return 0;
21 }
22 
23 int date_minus(Date *now,Date *birth)
24 {
25     
26     int days;
27     int year;
28 
29     if(now->year==birth->year)    //同一年的情况
30         return numOfYear(now)-numOfYear(birth)+1;
31     else if(now->year<birth->year)
32         return -1;
33 
34     //出生年的后几天
35     days=(isLeapYear(birth->year)?366:365)-numOfYear(birth)+1;
36 
37     //中间年
38     for(year=birth->year+1;year < now->year;year++)
39         days+=isLeapYear(year)?366:365;
40 
41     //今年的前几天
42     return days+numOfYear(now);
43 }
44 
45 //一年中的第几天
46 int numOfYear(Date *date)
47 {
48     int days=date->day;
49     switch(date->month-1)
50     {
51     case 11:days+=30;
52     case 10:days+=31;
53     case 9:days+=30;
54     case 8:days+=31;
55     case 7:days+=31;
56     case 6:days+=30;
57     case 5:days+=31;
58     case 4:days+=30;
59     case 3:days+=31;
60     case 2:days+=isLeapYear(date->year) ? 29 :28;
61     case 1:days+=31;
62         return days;
63     }
64     return -1;
65 }
66 
67 int isLeapYear(int year)
68 {
69     return (year%100 && year%4==0 )|| year%400==0;
70 }
days.c