c——根据天数输出日期

《c语言程序设计》（第三版）何钦铭 P190

 1 #include<stdio.h>
 2 void month_day(int year,int yearday,int *pmonth,int *pday);
 3 
 4 int main() {
 5     int day,month,year,yearday;
 6     printf("input year and yearday:");
 7     scanf("%d%d",&year,&yearday);
 8     month_day(year,yearday,&month,&day);
 9     printf("%d-%d-%d\n",year,month,day);
10     return 0;
11 }
12 
13 void month_day(int year,int yearday,int *pmonth,int *pday) {
14     int k,leap;
15     int tab[2][13]= {
16         {0,31,28,31,30,31,30,31,31,30,31,30,31},
17         {0,31,29,31,30,31,30,31,31,30,31,30,31},
18     };
19     leap = (year%4==0 && year%100!=0)||year%400==0;
20     for(k=1; yearday>tab[leap][k]; k++)
21         yearday-=tab[leap][k];
22     *pmonth=k;
23     *pday=yearday;
24 }

分析：

1、用指针实现了两个返回值

2、二维数组+变量判断闰年

3、20-21非常巧妙