#include <stdio.h>
int main() 
{
    int score = 101; //考试分数为87分  
    if(score<=100&&score>=0){
        switch(score/10)
        {
            case 10:
            case 9:
                printf("等级A");
                break;
            case 8:
                printf("等级B");
                break;
            case 7:
            case 6: 
                printf("等级C");
                break;
            default:
                printf("等级D");
                break;    
        }
    } else {
        printf("成绩出错（0~100）：%d",score);
    }
    return 0;
}

参考参考