一个支持大数计算的类型 仅不支持除法

#include<iostream>#include<cstdio>#include<cstring>#include<string>using namespace std;//一个完整的支持大数计算的类型//仅不支持除法int max(int a, int b) { return a > b ? a : b; }const int maxn = 1002;struct bign{      int len, s[maxn];      bign()      {          memset(s, 0, sizeof(s));          len = 1;      }      bign(int num)      {          *this = num;      }      bign(const char* num)      {          *this = num;      }      bign operator = (int num)      {          char s[maxn];          sprintf(s, "%d", num);          *this = s;          return *this;      }      bign operator = (const char* num)      {          len = strlen(num);          for(int i = 0; i < len; i++)          s[i] = num[len-i-1] - '0';          return *this;      }      string str() const      {          string res = "";          for(int i = 0; i < len; i++)          res = (char)(s[i] + '0') + res;          if(res == "") res = "0";          return res;      }      bign operator + (const bign& b) const                 //实现c+b的加法      {          bign c;          c.len = 0;          for(int i = 0, g = 0; g || i < max(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;          }          return c;      }      void clean()      {          while(len > 1 && !s[len-1]) len--;      }      bign operator * (const bign& b)      {          bign c; c.len = len + b.len;          for(int i = 0; i < len; i++)          for(int j = 0; j < b.len; j++)          c.s[i+j] += s[i] * b.s[j];          for(int i = 0; i < c.len-1; i++)          {              c.s[i+1] += c.s[i] / 10;              c.s[i] %= 10;          }          c.clean();          return c;      }    /*   bign operator / (int b)  {  bign c;  int j=1,s=0,i;  for(i=c.len-1;i>=0;i--)  {  int k=0;  for(s=s*10+c.s[i];s>=b;s-=b) k++;  c.s[i]=k;  }  return c;  }   */      bign operator - (const bign& b)      {          bign c; c.len = 0;          for(int i = 0, g = 0; i < len; i++)          {              int x = s[i] - g;              if(i < b.len) x -= b.s[i];              if(x >= 0) g = 0;              else              {                  g = 1;                  x += 10;              }              c.s[c.len++] = x;              }              c.clean();              return c;       }       bool operator < (const bign& b) const       {           if(len != b.len) return len < b.len;           for(int 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)       {           return !(b > *this);       }       bool operator == (const bign& b)       {           return !(b < *this) && !(*this < b);       }       bign operator += (const bign& b)       {           *this = *this + b;           return *this;       }};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;}