#include<stdio.h>
#include<string.h>
int main()
{
    int a,b,c,d,e,f,j;
    do{
        printf("输入a：");
        scanf("%d",&a);
        if(a<=0)
        printf("a是不多于5位的正整数");
    }while(a<=0||a>=100000);
    b=strlen(a);
    printf("它是%d位数",b);
    switch(b){
        case 1:printf("%d",b);break;
        case 2:c=a%10;
                  b=a%100;
                  printf("%d%d",c,b);
                  break;
          case 3:c=a%10;
                d=a%100;
                e=a%1000;
                printf("%d%d%d",c,d,e);
                break;
        case 4:c=a%10;
                d=a%100;
                e=a%1000;
                f=a%10000;
                printf("%d%d%d%d",c,d,e,f);
                break;
        case 5:c=a%10;
                d=a%100;
                e=a%1000;
                f=a%10000;
                j=a%100000;
                printf("%d%d%d%d%d",c,d,e,f,j);
                break;
        default:printf("出现未知错误");
    }
    return 0;
}

哦，谢谢啦。