程序代码：

#include<stdio.h>
int day_of_year(int year,int month,int day);
int main(void)

{
int year,day, month, unble, k, leap;
printf("请输入年月日:");
scanf("%d%d%d",&year,&month, &day);
unble=day_of_year(year,month,day);
printf("Unble=%d\n",unble);
return 0;
}


int day_of_year(int year, int month, int day)
{    int k, leap;
     int tab[2][13] = {
        { 0, 31, 28, 31, 30,31,30,31,31,30,31, 30,31 }
        { 0, 31, 29, 31, 30,31,30,31,31,30,31, 30,31 }
     };

     leap = (year%4==0 && year%100!=0) || year %400==0;)
     for ( k=1; k<month; k++ )
          day = day + tab[leap][k];
     return day;
}