程序是这样的  
main()
       {
       int num;
           char grade;
       printf("Please input score\n");

       scanf("%d",&num);
           num/=10;
           switch(num)
           {
               case 10:
               case 9:
                    grade='A';
                    break;
               case 8:
                    grade='B';
                    break;
               case 7:
                    grade='C';
                    break;
               case 6:
                    grade='D';
                    break;
               default:
                    grade='E';
                    break;
           }
       printf("%c\n",grade);
       }

switch不是不能用浮点数吗？怎么我输入96.5运行结果还是为A呢

switch是不能用浮点数 ,而且你也没有用浮点数, num是整形数, 输入96.5,实际值为 num = 96 , 然后num/=10;得到的数为9,整形参于除法运算,在默认下会将小数部分忽略掉,并没有四舍五入.所以得到的是9.

scanf("%d",&num); 这里已经转换为int型了

明白了谢谢啦

实际上就是截取了小数的整数部位