不失精度的阶乘算法

#include <iostream>
#include <vector>
int _tmain(int argc, _TCHAR* argv[])
{
using namespace std;
const _int64 LargeNumber=100000000;
vector<_int64> a(1,1);
_int64 i,n,temp,pro=0;
cout<<"input an integer:"<<endl;
cin>>n;
vector<_int64>::iterator iter;
for(i=1;i<=n;i++)
{
  for(iter=a.begin();iter!=a.end();++iter)
  {
   temp=(*iter)*i+pro;
   *iter=temp%LargeNumber;
   pro=temp/LargeNumber;
  }
  if(pro!=0)
   a.push_back(pro);
  pro=0;
}
for(iter=--(a.end());iter!=a.begin();--iter)
{

cout<<*iter<<" ";

cout.width(8);

cout.fill('0');

}

cout.width(8);

cout.fill('0');
cout<<*iter<<endl;
return 0;
}