程序代码：

#include<stdio.h>

void main() 
{
    int a = 0;
    scanf("%d", &a);
    if (a > 100) a += 10;

    switch (a / 10)
    {
        case 10:
        case 9:  printf("A");  break;
        case 8:  printf("B");   break;
        case 7:  printf("C");   break;
        case 6:  printf("D");  break;
        case 5:
        case 4:
        case 3:
        case 2:
        case 1:
        case 0:  printf("F");  break;
        default: printf("输入数据错误");
    }
    
}