我这是哪错了？请高手帮忙！谢谢！
#include <stdio.h>int main()
{float m;
printf("请你输入成绩：%f\n",m);
scanf("%f",&m);
while (m>100||m<0)
{printf("你输入的成绩有误，请重新输入：\n");
scanf("%f",&m);
}
switch ((int)(m/10))
{case 10:
case 9:printf("成绩相应等级为A\n");break;
case 8:printf("成绩相应等级为B\n");break;
case 7:printf("成绩相应等级为C\n");break;
case 6:printf("成绩相应等级为D\n");break;
case 5:
case 4:
case 3:
case 2:
case 1:
case 0:printf("成绩相应等级为E\n");}
return 0;
} 负数怎么来的？？
