c++高精度模板

#include <iostream>  
#include <stdio.h>  
#include <string.h>  
#include <math.h>  
#include <algorithm>  
#include <string>  
#include <vector>  
#include <list>  
using namespace std;  
  
const int maxn = 1000;  
  
struct bign  
{  
       int len, s[maxn];  //s是逆序存储  
       bign(){ memset(s, 0 , sizeof(s)); len = 1 ; } //构造函数  
       bign(int num) { *this  = num ; } //初始化  
       bign(const char* num) { *this = num ; }  
       string str() const  
       {  
           int i;  
           string res = "";  
           for( i = 0 ; i < len ; i++ )   
               res = (char)( s[i] + '0' ) + res ;  
           if (res == "") res = "0";  
           return res;  
       }   
          
       bign operator = (const char* num)  
       {  
            int i;  
            len = strlen(num);  
            for( i = 0 ; i < len ; i++ )  
                s[i] = num[len-i-1] - '0' ;  
            return *this;   
       }   
         
       bign operator = (int num)  
       {  
            char s[maxn];  
            sprintf(s , "%d" , num);  
            *this = s;  
            return *this;  
       }   
       //辅助函数 
	   void clean() { while(len > 1 && !s[len-1]) len--; }
       bign operator + (const bign& b) const  
       {  
            bign c;  
            c.len = 0;  
            int i, g;  
            for( i = 0 , g = 0 ; g || i < ( len > b.len ? len : b.len ) ; i++ )  
            {  
                 int x = g ;  
                 if( i < len ) x += s[i] ;  
                 if( i < b.len ) x += b.s[i] ;  
                 c.s[c.len++] = x % 10 ;  
                 g = x / 10 ;  
            }  
			c.clean();
            return c;  
       }  
	   bign operator+= (const bign &b)
		{
			 *this = *this + b;
			 return *this;
		}

       //比较的前提是两个数都没有前导零   
       bool operator < (const bign& b) const  
       {  
            if( len != b.len ) return len < b.len ;  
            int i;  
            for( i = len-1 ; i >= 0 ; i-- )  
                if( s[i] != b.s[i] ) return s[i] < b.s[i];  
            return false;  
       }  
       bool operator > (const bign& b) const { return b < *this; }  
       bool operator <= (const bign& b) const { return !(b < *this); }   
       bool operator >= (const bign& b) const { return !(*this < b); }   
       bool operator != (const bign& b) const { return b < *this || *this < b; }   
       bool operator == (const bign& b) const { return !(b < *this) || !(*this < b); }    
};  
  
istream& operator >> (istream &in , bign& x)  
{  
         string s;  
         in >> s;  
         x = s.c_str();  
         return in;  
}  
ostream& operator << (ostream &out , const bign& x)  
{  
         out << x.str();  
         return out;  
}