计算从开始日期到结束日期经过的天数

#include <stdio.h>

struct date {
int year;
int mon;
int day;
};

int days[13] = {[1] = 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

int getdays(struct date start, struct date end)
{
struct date tmp;
int x = end.year==start.year ? 0 : end.year-start.year-1;
x = 365*x + (x-(4-(start.year+1)%4)%4 + 3)/4 - (x-(100-(start.year+1)%100)%100+99)/100 + (x-(400-(start.year+1)%400)%400+399)/400;
for (tmp.year=start.year,tmp.mon=(start.mon-1)%12+1, tmp.day=-start.day;\
tmp.mon != end.mon || tmp.year!=end.year;
tmp.day += days[tmp.mon], tmp.mon/12&&(tmp.year=end.year),tmp.mon = tmp.mon%12+1 )
tmp.mon == 2 && !((tmp.year % 4 == 0 && tmp.year % 100 != 0) || tmp.year % 400 == 0) && tmp.day--;
return x+tmp.day+end.day;
}

int main(int argc, char **argv)
{
struct date start,end;
scanf("%d%d%d%d%d%d", &start.year, &start.mon, &start.day, &end.year, &end.mon, &end.day);
printf("%d\n", getdays(start, end));
return 0;
}