hdu1042计算10000以下数字的阶乘

半个小时看懂了大佬写的10行代码

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
const int maxn = 40000;
int f[40000];
int n;

int main()
{
    while(scanf("%d",&n)!=EOF)
    {
        memset(f,0,sizeof(f));
        f[0] = 1;
        for(int i = 2; i <= n; i++)
        {
            int c = 0;//低位来的进位
            for(int j = 0; j < maxn; j++)
            {
                int s = f[j]*i+c;
                f[j] = s%10;
                c = s/10;
            }
        }
        int flag = 0;
        for(int i = maxn-1; i >= 0; i--)
        {
            if(f[i]!=0)
            {
                flag = i;
                break;
            }
        }
        for(int j = flag; j >= 0; j--)
            printf("%d",f[j]);
        printf("\n");
    }
    return 0;
}