...

int main()
{
    int grade;
    printf("请输入成绩");
    scanf("%d",&grade);
    if(grade<0&&grade>100)
    {
        printf("输入错误");
    }
    if(grade>=90)
    {printf("A");
     } 
    else if(grade>=80&&grade<=89)
    {printf("B");
    }
    else if(grade>70&&grade<=79)
    {printf("C");
    }
    else if(grade>=60&&grade<=69)
    {printf("D");
    }
    else if(grade<60&&grade>=0)
    {printf("E");
    }
    return 0;
    }




  scanf("%d",&e);
   a=e/10000;
   b=e%10000/1000;
   c=e%100/10;
   d=e%10;
if(a==d&&b==c) 
{printf("这个五位数是回文数\n");
}
else
{
 printf("这个五位数不是回文数\n");
 } 
 return 0;
 }




int main()
{
 int grade;
 printf("请输入成绩");
 scanf("%d",&grade);
 switch(grade/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;
 case 5:
 case 4:
 case 3:
 case 2:
 case 1:
 case 0:printf("E/n");break;
 default:printf("error");
 }
    return 0;
 }

 scanf("%d",&a) ;
 if(a>=100000||a<0)
 {
  printf("error\n");
 }
 else
 {
    if(a>=10000&&a<99999)
  {
   b=a/10000;
   c=a/1000%10;
   d=a/100%10;
   e=a/10%10;
   f=a%10;
   g=f*10000+e*1000+d*100+c*10+b;
   printf("该数是五位数，逆序为%d\n",g) ;
  }
  else if(a>=1000&&a<9999)
  {
   b=a/1000;
   c=a/100%10;
   d=a/10%10;
   e=a/10;
   f=e*1000+d*100+c*10+b;
   printf("该数是四位数，逆序为%d\n",f);
  }
  else if(a>=100&&a<999)
  {
   b=a/100;
   c=a/10%10;
   d=a%10;
   e=d*100+c*10+b;
   printf("该数是三位数，逆序为%d\n",e);
  }
  else if(a>=10&&a<99)
  {
   b=a/10;
   c=a%10;
   d=c*10+b;
   printf("该数是二位数，逆序为%d\n",d);
  }
  else
  {
   printf("该数是一位数，逆序为%d\n",a);
  }
 }
 return 0;
}