结构体重载运算符的疑惑

#include
#include
#include
#include
using namespace std;
const int N = 1005;
struct bign
{
    int len,s[N];
    bign()  {  memset(s,0,sizeof(s));  len=1;  }
    bign(int num)  {  *this=num; }
    bign(char *num) { *this=num; }
    bign operator =(int num)
    {
        char c[N];
        sprintf(c,"%d",num);
        *this=c;
        return *this;
    }
    bign operator =(const char *num)
    {
        len=strlen(num);
        for (int i=0;i1&&!s[len-1]) len--;
    }
    bign operator +(const bign &b)
    {
        bign c;    
        c.len=0;
        for (int i=0,g=0;g||i=0) g=0;
            else{          
                x+=10;
                g=1;
            };
            c.s[c.len++]=x;
        }
        c.clean();
        return c;
    }
    bign operator *(const bign &b)
    {
        bign c;
        c.len=len+b.len;
        for (int i=0;i=0;i--)
             if (s[i]!=b.s[i]) return s[i]>(istream &in,bign &x)
{
  string s;
  in>>s;
  x=s.c_str();
  return in;
}
ostream& operator <<(ostream &out,bign &x)
{
    out<>a>>b;
//    cout<

bign(int num)  {  *this=num; }
bign(char *num) { *this=num; }

bign n=123;

bign n;
n=123;