#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;
}

strlen不能获得int类型变量长度，你得自己写程序得到数据位数。

哦，谢谢啦。

不用那么复杂

#include<stdio.h>

int f(int s)
{
    static int t=0;
    if(s==0) return t;
    int m=s%10;
    ++t;
    f(s/=10);
    printf("%4d",m);
    return t;
}
int main()
{
    int t=f(123456789);
    printf("\n他是一个%2d位数。\n",t);
    return 0;
}

[此贴子已经被作者于2015-11-3 15:56编辑过]

#include<stdio.h>
#include<math.h>
main()
{   
    int a,b,c,d,e,f;
    printf("请输入一个不大于五位数的数字\n");
    scanf("%d",&a);
    if (a>99999)printf("数值错误\n");
    else {
           b=a/10000;
           c=a/1000-b*10;
           d=a/100-b*100-c*10;
           e=a/10-b*1000-c*100-d*10;
           f=a-b*10000-c*1000-d*100-e*10;
      
                  if (b>0)printf("输入的是五位数%d,%d,%d,%d,%d\n",b,c,d,e,f),printf("%d,%d,%d,%d,%d\n",f,e,d,c,b);
               else if (c>0)printf("输入的是四位数%d,%d,%d,%d\n",c,d,e,f),printf("%d,%d,%d,%d\n",f,e,d,c);
               else if (d>0)printf("输入的是三位数%d,%d,%d\n",d,e,f),printf("%d,%d,%d\n",f,e,d);
               else if (e>0)printf("输入的是二位数%d,%d\n",e,f),printf("%d,%d\n",f,e);
               else printf("输入的是个位数%d\n",f),printf("%d\n",f);
   
    }
}

strlen不能获得int类型变量长度，你得自己写程序得到数据位数。

printf()函數的返回値就是數據位數了。

#include <stdio.h>
#include <conio.h>

int main(void)
{
    int x = 54321;
    int length;

    length = printf_s("%d", x);
    printf_s("的位數是%d\n", length);

    printf_s("\nPress any key to continue...");
    _getch();
    return 0;
}

代码不通用