very_long_int

#include <iostream>
#include <algorithm>
#include <string>
#include <deque>

using namespace std;

class very_long_int{
 friend istream& operator>>(istream& instream,very_long_int& very_long);
 friend ostream& operator<<(ostream& outstream,const very_long_int very_long);
public:
 very_long_int operator + (const very_long_int& other_number);
 very_long_int operator * (const very_long_int& other_number);
 very_long_int operator =(very_long_int& other_number);
 very_long_int factor(int i);
    deque<char> digist;
 char least(unsigned i) const;

};

istream& operator >> (istream& instream,very_long_int& very_long)
{
 const char LOWEST_DIGIST_CHAR = '0';
 const char HIGHEST_DIGIST_CHAR = '9';
 const char SENTINEL = 'X';

 char digist_char;

 very_long.digist.erase(very_long.digist.begin(),very_long.digist.end());

 do
 {
  instream >> digist_char;
  if ( (LOWEST_DIGIST_CHAR<= digist_char) && (digist_char <= HIGHEST_DIGIST_CHAR))
   very_long.digist.push_back(digist_char - LOWEST_DIGIST_CHAR);
 } while (digist_char != SENTINEL);

 return instream;
}

ostream& operator<<(ostream& outstream,const very_long_int very_long)
{
 for (unsigned i =0;i<very_long.digist.size();++i)
  outstream<<(int)very_long.digist[i];
 return outstream;
}//重载<<

very_long_int very_long_int::operator =(very_long_int& other_number) //赋值
{
 digist.erase(digist.begin(),digist.end());
 for(unsigned i=0;i<other_number.digist.size();i++)
  digist.push_back(other_number.digist[i]);
 return *this;
}

very_long_int very_long_int::operator +(const very_long_int &other_number)
{
 unsigned carry = 0,
  large_size,
  partial_sum;
 very_long_int sum;
 if (digist.size() > other_number.digist.size())
  large_size = digist.size();
 else
  large_size = other_number.digist.size();
 for (unsigned i =0;i < large_size;++i)
 {
  partial_sum = least(i) + other_number.least(i) + carry;
  carry = partial_sum/10;
  sum.digist.push_back(partial_sum%10);
 }//for
 if (carry == 1)
  sum.digist.push_back(carry);
 reverse(sum.digist.begin(),sum.digist.end());
 return sum;
}//重载+

very_long_int very_long_int::operator *(const very_long_int& other_number)
{
 unsigned carry=0;
 very_long_int result ,temp;

 for(unsigned i=0;i<other_number.digist.size();i++)
 {
  temp.digist.erase(temp.digist.begin(),temp.digist.end());
  carry=0;
  for(unsigned j=0;j<digist.size();j++)
  {
   unsigned n=least(j)*other_number.least(i)+carry;
   carry=n/10;
   temp.digist.push_front(n%10);
  }
  if(carry!=0) temp.digist.push_front(carry);
  for(unsigned k=0;k<i;k++) temp.digist.push_back(0);
  //cout<<"temp:"<<temp<<endl;
  result=result+temp;
 }
 return result;
} //重载*

//计算阶乘的算法
very_long_int very_long_int::factor(int i){
 very_long_int r1,r,result;
 r1.digist.push_back(1);
 r.digist.push_back(1);
 result.digist.push_back(1);
 if (i<=1)
  return r1;
 for (int k = 2;k <=i;++k)
 {
  r = r + r1;
  result = result * r;
 }
 return result;
}

char very_long_int::least(unsigned i) const
{
 if (i >= digist.size())
  return 0;
 else
  return digist[digist.size() - i - 1];
}//least

void   main()  
{  
 very_long_int   myVeryLongInt1,   myVeryLongInt2;  
 cout   <<   "Please   input   your   very   long   int1:   "<<endl;  
 cin   >>   myVeryLongInt1;   //注意very_long_int的结束符是X
 cout   <<"Please   input   your   very   long   int2:   "<<endl;  
 cin   >>   myVeryLongInt2;  
 cout   <<"int1   +   int2   =   "   <<   myVeryLongInt1   +   myVeryLongInt2   <<   endl;
 cout   <<"int1   *   int2   =   "   <<   myVeryLongInt1   *   myVeryLongInt2   <<   endl;
 very_long_int num;
 int n ;
 cout<<"输入要求的阶乘(n是正整数)n:";
 cin>>n;
 cout<<n<<"的阶乘是："<<num.factor(n)<<endl;
}