switch语句应该实现不了这个功能

因为switch语句后面必须是常量 不能是变量

#include <stdio.h>
#include <conio.h>
int main(void){
int a;
scanf("%d", &a);
if(a>100||a<0){printf("error");return 0;}
switch(a){
case 100:{printf("A");break;}
case 99:{printf("A");break;}
case 98:{printf("A");break;}
case 97:{printf("A");break;}
case 96:{printf("A");break;}
case 95:{printf("A");break;}
case 94:{printf("A");break;}
case 93:{printf("A");break;}
case 92:{printf("A");break;}
case 91:{printf("A");break;}
case 90:{printf("A");break;}
case 89:{printf("B");break;}
case 88:{printf("B");break;}
case 87:{printf("B");break;}
case 86:{printf("B");break;}
case 85:{printf("B");break;}
case 84:{printf("B");break;}
case 83:{printf("B");break;}
case 82:{printf("B");break;}
case 81:{printf("B");break;}
case 80:{printf("B");break;}
case 79:{printf("C");break;}
case 78:{printf("C");break;}
case 77:{printf("C");break;}
case 76:{printf("C");break;}
case 75:{printf("C");break;}
case 74:{printf("C");break;}
case 73:{printf("C");break;}
case 72:{printf("C");break;}
case 71:{printf("C");break;}
case 70:{printf("C");break;}
case 69:{printf("D");break;}
case 68:{printf("D");break;}
case 67:{printf("D");break;}
case 66:{printf("D");break;}
case 65:{printf("D");break;}
case 64:{printf("D");break;}
case 63:{printf("D");break;}
case 62:{printf("D");break;}
case 61:{printf("D");break;}
case 60:{printf("D");break;}
default:{printf("E");break;}
}
return 0;
}

#include <stdio.h>
#include <stdlib.h>
/* run this program using the console pauser or add your own getch, system("pause") or input loop */
int main()
{
int x;
printf("输入一个成绩:\n");
printf("\n");
scanf("%d",&x);
if(x<=0)
{
printf("成绩过小请重新输入!\n");
scanf("%d",&x);
}
else if(x>100)
{
printf("成绩过大请重新输入！\n");
printf("\n");
scanf("%d",&x);
}
switch(x/10)
{
case 10:
printf("A");
break;
case 9:
printf("A");
break;
case 8:
printf("B");
break;
case 7:
printf("C");
break;
case 6:
printf("D");
break;
default:
printf("error!\n");
}
return 0;
}