//问题八：输入年、月、日，在屏幕上输出此日期是该年的第几天
#include<stdio.h>
int main()
{
    int year,month,day,what_day;
 //   int a[130],b[130];
    int a[13]={0,31,29,31,30,31,30,31,31,30,31,30,31};
    int b[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
    scanf("%d,%d,%d",year,month,day);
    if(year%4==0)
        {
            for(;month>0;month--)
                what_day+=a[month];
            printf("\n%d",what_day);
        }
    else
        {
            for(;month>0;month--)
                what_day+=b[month];
            printf("\n%d",what_day);
        }
    what_day+=day;
  //  printf("\n第%d天",what_day);
    return 0;
}

多加一个月

scanf("%d,%d,%d",&year,&month,&day);

明白了，谢谢了诸位