#include<stdio.h>
int main()
{
   int i=1;
   float score,max,min,sum,ave;
   printf("Please input a grade!\n");
   scanf("%f",score);
   max=min=sum=score;
   while(score!=-1)
   {
         printf("Please input another grade!\n");
     scanf("%f",score);
     if(score>max)
            max=score;
         if(score<min&&score!=-1)
            min=score;
         sum+=score;
         i++;
    }
   sum=sum+1;
   ave=sum/(i-1);
   printf("max=%6.2f,min=%6.2f,aver=%6.2f\n",max,min,ave);
   return 0;
}

一旦运行，就显示"应用程序错误，内存不能为written"

scanf("%f",score);

额，原来如此，谢了。