hdu 2399

#include<cstdio>#define maxn 10000int main(){    double sum=0,j=0;    int f=1,i=0;    char a[maxn];    while(gets(a)!=NULL)    {        f=1;sum=0;j=0;        for(i=0;a[i];i++)        {            if(a[i]=='A'||a[i]=='B'||a[i]=='C'||a[i]=='D')            {                sum+=4-(a[i]-65);                j++;            }            else if(a[i]=='F')            {                sum+=0;                j++;            }            else if(a[i]==' ')//缺少这个则错误。？                    continue;            else            {                printf("Unknown letter grade in input\n");                f=0;                break;            }        }        if(f==1)            printf("%.2lf\n",sum/j);    }    return 0;}