#include<stdio.h>
int sum(long num)  /*求一个十进制6位正整数各位数字之和*/
{
        long a = 0, b = 0, len;
        int sum = 0;
        for(len = 100000; len > 0; len = len / 10) {
                a = num / len;
                b = num % len;
                sum = sum + a;
                num = b;
        }
        return sum;
}

int main()
{
        int a;
        long num;
        scanf("%l", &num);
        printf("%d", sum(num));
}
问题是出在for语句块里面，但我不知道是什么问题，望高手能给我解答.

2楼，能否解答下scanf("%li",&n);里的%li为什么能编译通过？书上怎么没有这个啊？