食用注意事项

1. 减法如果是负数会返回负数的绝对值
2. 乘法只有高精乘以低精, 也就是 Biginteger * long long
3. 除法只有高精除以低精, 也就是 Biginteger / long long

代码

#include <iostream>
#include <vector>
#include <algorithm>
#include <cstring>
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.size() - 1) / WIDTH + 1;
        for (int i = 0; i < len; i++) {
            int end = str.size() - 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) {
        BigInteger c;
        c.s.clear();
        int t = 0;
        for (int i = 0; i < s.size() || i < b.s.size(); i ++) {
            if (i < s.size()) t += s[i];
            if (i < b.s.size()) t += b.s[i];
            c.s.push_back(t % BASE);
            t /= BASE;
        }
        if(t) c.s.push_back(t);
        return c;
    }

    bool operator< (const BigInteger& b) {
        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;
    }

    BigInteger operator- (const BigInteger& b) {
        if (*this < b) {
            return sub(b, *this);
        } else {
            return sub(*this, b);
        }
    }

    // a >= b
    BigInteger sub(const BigInteger& a ,const BigInteger& b) {
        BigInteger c;
        c.s.clear();
        for (int t = 0, i = 0; i < a.s.size(); i ++) {
            t = a.s[i] - t;
            if (i < b.s.size()) t -= b.s[i];
            c.s.push_back((t + BASE) % BASE);
            if (t < 0) t = 1;
            else t = 0;
        }
        while(c.s.size() > 1 && c.s.back() == 0) c.s.pop_back();
        return c;
    }

    BigInteger operator* (const long long& b) {
        BigInteger c;
        c.s.clear();
        for (int t = 0, i = 0; i < s.size() || t; i ++) {
            if (i < s.size()) t += s[i] * b;
            c.s.push_back(t % BASE);
            t /= BASE;
        }
        while(c.s.size() > 1 && c.s.back() == 0) c.s.pop_back();
        return c;
    }

    BigInteger operator/ (const int& b) {
        BigInteger c;
        c.s.clear();
        for (int t = 0, i = s.size() - 1; i >= 0; i--) {
            t = t * BASE + s[i];
            c.s.push_back(t / b);
            t %= b;
        }
        reverse(c.s.begin(), c.s.end());
        while(c.s.size() > 1 && c.s.back() == 0) c.s.pop_back();
        return c;
    }
};

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;
}

int main()
{
    BigInteger a = 1000, b = 2000;
    int c = 3;
    cout << a + b << endl;
    cout << a - b << endl;
    cout << a * c << endl;
    cout << a / c << endl;
    return 0;
}