高精度bign模板(暂定+-*)

# include<cstdio>
# include<cstring>
# include<string>
# include<iostream>

using namespace std;

const int maxn = 1000;

struct bign
{
    int len, s[maxn];

    bign() {memset(s,0,sizeof(s));len=1;}//struct构造函数， 必须与类名同名

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

    bign operator = (const char * num){
        len = strlen(num);
        for(int 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;
    }

    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{
        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 - (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;
    }

    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(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;
}
int main(void)
{
    bign a, b;
    cin>>a;
    cin>>b;
    cout<<"a+b="<<a+b<<endl<<"a-b="<<a-b<<endl<<"a*b="<<a*b<<endl;

    return 0;
}