scanf("%f,&score");可要改为scanf("%f",&score);这是我的观点！

score = (score - score%10) /10

switch(score)

刚学，也来凑凑热闹

把你们的改了下 试试也挺好用
main()
{
float score ;int c=0;
char grade ;
printf("please input a score\n");
while(1){
scanf("%f",&score);
if(score<0)
break;
if(score>=90)
c=1;
if((score>=60)&&(score<90))
c=2;
if(score<60)
c=3;
switch(c)
{
case 1 :
printf("%f",score);
printf("belong to grade=A\n");break;
case 2 :
printf("%f",score);printf("belong tograde=B\n");break;
default:
printf("%f",score);
printf("grade=C\n");
break;
}

#include"stdio.h"
void main()
{
int n,score ;
char grade ;
printf("please input a score\n");
scanf("%d",&score);
n=score/10;

switch(n)
{
case 9:printf("'A'");break;
case 8:
case 7:
case 6:printf("'B'");break;
default: printf("'C'");
}
}

毛病有点多哦!!语法还需要加强

n=（int)score/30
n做标号就行了嘛
或者多加个int m
让m=score/30,就可以了，标号3→A，2→B，其余的C

#include <stdio.h>

void main()
{
float score;
char grade;
int m;

printf("please input score: \n");
scanf("%f",&score);

m=score/30;
switch(m)
{
case 3 : grade='A';
break;
case 2 : grade='B';
break;
default: grade='C';
break;
}

printf("%f belongs to c%.\n",score,grade);
}

不错啊！看来是有些进步啊！