大整数类

#include
#include
#include
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;
    }

    BigInteger operator + (const BigInteger& b) const
    {
        BigInteger c;
        c.s.clear();
        for (int i = 0, 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)
    {
        *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 false;
    }
    bool operator <=(const BigInteger& b) const
    {
        return !(b < *this);
    }
    bool operator >=(const BigInteger& b) const
    {
        return !(*this < b);
    }
    bool operator !=(const BigInteger& b) const
    {
        return !(b < *this)|| !(*this < b);
    }
};
ostream& operator << (ostream &out, const BigInteger& 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;
}