大整数类模板

#include <iostream>
#include <cstdio>
#include <sstream>
#include <vector>
using namespace std;

struct BigInteger {
    static const int BASE=100000000;
    static const int WIDTH=8;
    vector<int> s;
    
    BigInteger(long long num=0) { *this=num; }
    BigInteger operator =(long long num) {
        s.clear();
        do {
            s.push_back(num%BASE);
            num/=BASE;
        } while (num>0);
        return *this;
    }
    BigInteger operator =(const string& str) {
        s.clear();
        int x, len=(str.length()-1)/WIDTH+1; 
        for (int i=0; i<len; i++) {
            int end=str.length()-i*WIDTH;
            int start=max(0, end-WIDTH);
            sscanf(str.substr(start, end-start).c_str(), "%d", &x);
            s.push_back(x);
        }
        return *this;
    }
    
    ostream& operator << (ostream &out, const BigInter& x) {
        out<<x.s.back();
        for (int i=x.s.size()-2; i>=0; i--) {
            char buf[20];
            sprintf(buf, "%08d", x.s[i]);
            for (int j=0; j<strlen(buf); j++) out<<buf[j];
        }
        return out;
    }
    
    istream& operator >> (istream &in, BigInteger& x) {
        string s;
        if (!(in>>s)) return in;
        x=s;
        return in;
    }
    
    BigInteger operator + (const BigInteger& b) const {
        BigInteger c;
        c.s.clear();
        for (int i=1, g=0; ; i++) {
            if (g==0 && i>=s.size() && i>=b.s.size()) break;
            int x=g;
            if (i<s.size()) x+=s[i];
            if (i<b.s.size()) x+=b.s[i];
            c.s.push_back(x%BASE);
            g=x/BASE;
        }
        return c;
    }
    BigInteger operator += (const BigInteger& b) const {
        *this=*this+b; return *this;
    }
    
    bool operator < (const BigInteger& b) const {
        if (s.size()!=b.s.size()) return s.size()<b.s.size();
        for (int i=s.size()-1; i>=0; i--)
            if (s[i]!=b.s[i]) return s[i]<b.s[i];
        return 0;
    }
    bool operator > (const BigInteger& b) { return b<*this; }
    bool operator <= (const BigInteger& b) { return !(b<*this); }
    bool operator >= (const BigInteger& b) { return !(b>*this); }
    bool operator != (const BigInteger& b) { return (b>*this || b<*this); }
    bool operator != (const BigInteger& b) { return (!(b>*this) && !(b<*this)); }
};