HOJ ( acm.hdu.edu.cn ) 1042

#include <iostream>
#include <string>
#include <deque>
using namespace std;
class unsigned_big_integer{
protected:
   typedef unsigned_big_integer class_type;
   typedef unsigned long celltype;
   std::deque<celltype> m_num;      //大数的内部储存结构
public:
   unsigned_big_integer(const unsigned long integer):m_num(){
       unsigned long x=integer;
       while(x){
           m_num.push_front(x%10);
           x/=10;
       }
   }
   virtual ~unsigned_big_integer(){}

   class_type& operator=(const class_type& bi){
       this->m_num=bi.m_num;
       return *this;
   }
public:
   virtual std::string str(){      //转换成字符串(用于输出)
       std::string s(m_num.begin(),m_num.end());
       for(std::string::iterator itr=s.begin();itr!=s.end();++itr)
           *itr+='0';
       return s;
   }
   virtual class_type& operator*=(unsigned long const x){
       //
       // 以 12345 * 12 作为例子，算法如下
       //
       //    12345
       // *     12
       //   _______
       //       60   (5*12)
       //      48    (4*12)
       //     36     (3*12)
       //    24      (2*12)
       //   12       (1*12)
       //  _________
       //   148140
       //
       for(std::deque<celltype>::iterator itr=m_num.begin();itr!=m_num.end();++itr)
           *itr*=x;
       for(std::deque<celltype>::reverse_iterator ritr=m_num.rbegin();ritr!=m_num.rend()-1;++ritr){
           *(ritr+1)+=(*ritr)/10;
           *ritr%=10;
       }
       while(m_num.front()>=10){
           celltype x=m_num.front()/10;
           m_num.front()%=10;
           m_num.push_front(x);
       }
       return *this;
   }
};

int main()
{
   for(int n;cin>>n;cout<<endl) {
       if (n>=11) {
           unsigned_big_integer ans(n);
           for(;--n;)
               ans*=n;
           std::operator<<(cout,ans.str());
       } else {
           unsigned long ans=1;
           for(;n;--n) //VC 会错误解释 for(;n--;) 的意思
               ans*=n;
           cout<<ans;
       }
   }
   return 0;
}