紫书：

#include 
    
       #include 
     
        #include 
      
         #include 
       
          using namespace std;  const int maxn = 1000;  struct bign{      int d[maxn], len;      void clean() { while(len > 1 && !d[len-1]) len--; }      bign()          { memset(d, 0, sizeof(d)); len = 1; }      bign(int num)   { *this = num; }       bign(char* num) { *this = num; }      bign operator = (const char* num){          memset(d, 0, sizeof(d)); len = strlen(num);          for(int i = 0; i < len; i++) d[i] = num[len-1-i] - '0';          clean();          return *this;      }      bign operator = (int num){          char s[20]; sprintf(s, "%d", num);          *this = s;          return *this;      }      bign operator + (const bign& b){          bign c = *this; int i;          for (i = 0; i < b.len; i++){              c.d[i] += b.d[i];              if (c.d[i] > 9) c.d[i]%=10, c.d[i+1]++;          }          while (c.d[i] > 9) c.d[i++]%=10, c.d[i]++;          c.len = max(len, b.len);          if (c.d[i] && c.len <= i) c.len = i+1;          return c;      }      bign operator - (const bign& b){          bign c = *this; int i;          for (i = 0; i < b.len; i++){              c.d[i] -= b.d[i];              if (c.d[i] < 0) c.d[i]+=10, c.d[i+1]--;          }          while (c.d[i] < 0) c.d[i++]+=10, c.d[i]--;          c.clean();          return c;      }      bign operator * (const bign& b)const{          int i, j; bign c; c.len = len + b.len;           for(j = 0; j < b.len; j++) for(i = 0; i < len; i++)               c.d[i+j] += d[i] * b.d[j];          for(i = 0; i < c.len-1; i++)              c.d[i+1] += c.d[i]/10, c.d[i] %= 10;          c.clean();          return c;      }      bign operator / (const bign& b){          int i, j;          bign c = *this, a = 0;          for (i = len - 1; i >= 0; i--)          {              a = a*10 + d[i];              for (j = 0; j < 10; j++) if (a < b*(j+1)) break;              c.d[i] = j;              a = a - b*j;          }          c.clean();          return c;      }      bign operator % (const bign& b){          int i, j;          bign a = 0;          for (i = len - 1; i >= 0; i--)          {              a = a*10 + d[i];              for (j = 0; j < 10; j++) if (a < b*(j+1)) break;              a = a - b*j;          }          return a;      }      bign operator += (const bign& b){          *this = *this + b;          return *this;      }      bool operator <(const bign& b) const{          if(len != b.len) return len < b.len;          for(int i = len-1; i >= 0; i--)              if(d[i] != b.d[i]) return d[i] < b.d[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) && !(b > *this);}      string str() const{          char s[maxn]={};          for(int i = 0; i < len; i++) s[len-1-i] = d[i]+'0';          return s;      }  };  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;  }
       
      
     
    

最全：

#include
    
     #include
     
      #include
      
       #include
       
        #include
        
         #include
         
          #include
          
           #include
           
            using namespace std;const int MAX_L=2005; //最大长度，可以修改class bign{public: int len, s[MAX_L];//数的长度，记录数组//构造函数 bign(); bign(const char*); bign(int); bool sign;//符号 1正数 0负数 string toStr() const;//转化为字符串，主要是便于输出 friend istream& operator>>(istream &,bign &);//重载输入流 friend ostream& operator<<(ostream &,bign &);//重载输出流//重载复制 bign operator=(const char*); bign operator=(int); bign operator=(const string);//重载各种比较 bool operator>(const bign &) const; bool operator>=(const bign &) const; bool operator<(const bign &) const; bool operator<=(const bign &) const; bool operator==(const bign &) const; bool operator!=(const bign &) const;//重载四则运算 bign operator+(const bign &) const; bign operator++(); bign operator++(int); bign operator+=(const bign&); bign operator-(const bign &) const; bign operator--(); bign operator--(int); bign operator-=(const bign&); bign operator*(const bign &)const; bign operator*(const int num)const; bign operator*=(const bign&); bign operator/(const bign&)const; bign operator/=(const bign&);//四则运算的衍生运算 bign operator%(const bign&)const;//取模（余数） bign factorial()const;//阶乘 bign Sqrt()const;//整数开根（向下取整） bign pow(const bign&)const;//次方//一些乱乱的函数 void clean();};#define max(a,b) a>b ? a : b#define min(a,b) a
            >(istream &in, bign &num){ string str; in>>str; num=str; return in;}ostream &operator<<(ostream &out, bign &num){ out<
             
              = 0; i--) if (s[i] != num.s[i]) return sign ? (s[i] < num.s[i]) : (!(s[i] < num.s[i])); return !sign;}bool bign::operator>(const bign&num)const{ return num < *this;}bool bign::operator<=(const bign&num)const{ return !(*this>num);}bool bign::operator>=(const bign&num)const{ return !(*this
              
                num || *this < num;}bool bign::operator==(const bign&num)const{ return !(num != *this);}bign bign::operator+(const bign &num) const{ if (sign^num.sign) { bign tmp = sign ? num : *this; tmp.sign = 1; return sign ? *this - tmp : num - tmp; } bign result; result.len = 0; int temp = 0; for (int i = 0; temp || i < (max(len, num.len)); i++) { int t = s[i] + num.s[i] + temp; result.s[result.len++] = t % 10; temp = t / 10; } result.sign = sign; return result;}bign bign::operator++(){ *this = *this + 1; return *this;}bign bign::operator++(int){ bign old = *this; ++(*this); return old;}bign bign::operator+=(const bign &num){ *this = *this + num; return *this;}bign bign::operator-(const bign &num) const{ bign b=num,a=*this; if (!num.sign && !sign) { b.sign=1; a.sign=1; return b-a; } if (!b.sign) { b.sign=1; return a+b; } if (!a.sign) { a.sign=1; b=bign(0)-(a+b); return b; } if (a
               
                = 0) g = 0; else { g = 1; x += 10; } result.s[result.len++] = x; } result.clean(); return result;}bign bign::operator * (const bign &num)const{ bign result; result.len = len + num.len; for (int i = 0; i < len; i++) for (int j = 0; j < num.len; j++) result.s[i + j] += s[i] * num.s[j]; for (int i = 0; i < result.len; i++) { result.s[i + 1] += result.s[i] / 10; result.s[i] %= 10; } result.clean(); result.sign = !(sign^num.sign); return result;}bign bign::operator*(const int num)const{ bign x = num; bign z = *this; return x*z;}bign bign::operator*=(const bign&num){ *this = *this * num; return *this;}bign bign::operator /(const bign&num)const{ bign ans; ans.len = len - num.len + 1; if (ans.len < 0) { ans.len = 1; return ans; } bign divisor = *this, divid = num; divisor.sign = divid.sign = 1; int k = ans.len - 1; int j = len - 1; while (k >= 0) { while (divisor.s[j] == 0) j--; if (k > j) k = j; char z[MAX_L]; memset(z, 0, sizeof(z)); for (int i = j; i >= k; i--) z[j - i] = divisor.s[i] + '0'; bign dividend = z; if (dividend < divid) { k--; continue; } int key = 0; while (divid*key <= dividend) key++; key--; ans.s[k] = key; bign temp = divid*key; for (int i = 0; i < k; i++) temp = temp * 10; divisor = divisor - temp; k--; } ans.clean(); ans.sign = !(sign^num.sign); return ans;}bign bign::operator/=(const bign&num){ *this = *this / num; return *this;}bign bign::operator%(const bign& num)const{ bign a = *this, b = num; a.sign = b.sign = 1; bign result, temp = a / b*b; result = a - temp; result.sign = sign; return result;}bign bign::pow(const bign& num)const{ bign result = 1; for (bign i = 0; i < num; i++) result = result*(*this); return result;}bign bign::factorial()const{ bign result = 1; for (bign i = 1; i <= *this; i++) result *= i; return result;}void bign::clean(){ if (len == 0) len++; while (len > 1 && s[len - 1] == '\0') len--;}bign bign::Sqrt()const{ if(*this<0)return -1; if(*this<=1)return *this; bign l=0,r=*this,mid; while(r-l>1) { mid=(l+r)/2; if(mid*mid>*this) r=mid; else l=mid; } return l;}bign num0,num1,res;int main() { num0 = 1, num1 = 2; res=num0-num1; cout << res << endl; return 0;}
               
              
             
           
          
         
        
       
      
     
    

出处：

紫书和