#include<stdio.h>int main(){   int grade;  printf("请输入成绩");  scanf("%d",&grade);  if(grade<0||grade>100)  {printf("wrong");}  switch(grade/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:printf("不及格");break;  }   return 0;}

#include<stdio.h>int main(){    int a,b,c,d,e;    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");    }    else    {        printf("这个五位数不是回文数");    }    return 0;}

#include<stdio.h>int main(){        int a,b,c,d,e,f,g;    scanf("%d",&a);    if(a>=100000||a<0)    {        printf("error\n");    }    else     {        if(a>=10000&&a<9999)        {            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;}