C :

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
  int n;
  while(scanf("%d",&n)!=EOF)
  {
      if(n<0||n>100)  {printf("Score is error!\n");continue;}
      switch(n/10){
             case 10:
             case 9:printf("A\n");break;
             case 8:printf("B\n");break;
             case 7:printf("C\n");break;
             case 6:printf("D\n");break;
             default:printf("E\n");break;                                    
             } 
  }
  return 0;
}

C++ :

#include "stdio.h"
int main()
{
	int score;
	while(scanf("%d",&score)!=EOF){
		if((score>=0)&&(score<=100)){
			switch(score/10){
            case 10:printf("A\n");break;
            case 9:printf("A\n");break;
            case 8:printf("B\n");break;
            case 7:printf("C\n");break;
            case 6:printf("D\n");break;
            default:printf("E\n");break;
			}
		}
		else
			printf("Score is error!\n");
	}
	return 0;
}