高精度运算

#include<iostream>
#include<string.h>
using namespace std;
const int max=1000;
struct bign
{
 int len,s[max];
 bign()
 {
  memset(s,0,sizeof(s));
  len=1;
 }
 bign operator = (const char * num)
 {
  len=strlen(num);
  for(int i=0;i<len;i++)s[i]=num[len-1-i]-'0';
  return *this;
 }
      bign operator = (int num)
 {
  char s[max];
  sprintf(s,"%d",num);
  *this=s;
  return *this;
 }
   bign(int num){*this=num;}
   bign(const char *num){*this=num;}
   string str() const
   {
    string res=" ";
    for(int i=0;i<len;i++)
     res=((char)(s[i]+'0'))+res;
    if(res==" ") res="0";
    return res;
   }
   //friend istream& operator >>(istream &in,bign &x);
      //friend ostream& operator <<(ostream &out,const bign &x);
};
/*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;
}*/
int main()
{
 bign x;
 x="123456789";
 //cin>>x;
 return 0;
}