1)计算从1990年1月1日开始至指定日期共有多少天；
2)由于“打鱼”和“晒网”的周期为5天，所以将计算出的天数用5去除；
3)根据余数判断他是在“打鱼”还是在“晒网”；
若 余数为1，2，3，则他是在“打鱼”
否则 是在“晒网”
#include<stdio.h>
int days(struct date day);
struct date{
int year;int month;int day;
};
int main()
{
struct date today,term;
int yearday,year,day;
printf("Enter year/month/day:");
scanf("%d%d%d",&today.year,&today.month,&today.day);
term.month=12;
term.day=31;
for(yearday=0,year=1990;year<today.year;year++)
{
term.year=year;
yearday+=days(term);
}
yearday+=days(today);
day=yearday%5;
if(day>0&&day<4) printf("he was fishing at that day.\n");
else printf("He was sleeping at that day.\n");
return 0;
}
int days(struct date day)
{
static int day_tab[2][13]={{0,31,28,31,30,31,30,31,31,30,31,30,31,}, /*平均每月的天数*/
{0,31,29,31,30,31,30,31,31,30,31,30,31,},};
int i,lp;
lp=((day.year%4==0&&day.year%100!=0)||day.year%400==0);/*判定year为闰年还是平年，lp=0为平年，非0为闰年*/
for(i=1;i<day.month;i++) /*计算本年中自1月1日起的天数*/
day.day+=day_tab[lp][i];
return day.day;
}