简单版高精度

#include <bits/stdc++.h>
using namespace std;

struct bigint {
    int d[1000];
    int len;
    bigint() : len(0) {
        memset(d, 0, sizeof(d));
    }
    void fix() {
        while (len >= 2 && d[len - 1] == 0) len--;
    }
    bool operator < (const bigint &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 0;
    }

};

bigint change(string s) {
    bigint a;
    a.len = (int)s.length();
    for (int i = 0; i < a.len; i++){
        a.d[i] = s[a.len - i - 1] - '0';
    }
    return a;
}
bigint change(long long x) {
    string s = to_string(x);
    return change(s);
}

bigint operator + (const bigint &a, const bigint &b) {
    bigint c;
    int carry = 0;
    for (int i = 0; i < a.len || i < b.len; i++) {
        int tmp = a.d[i] + b.d[i] + carry;
        c.d[c.len++] = tmp % 10;
        carry = tmp / 10;
    }
    if (carry) c.d[c.len++] = carry;
    return c;
}

bigint operator - (const bigint &a, const bigint &b) {
    bigint c = a;
    for (int i = 0; i <= b.len; i++) {
        if (i != b.len) c.d[i] -= b.d[i];
        while (c.d[i] < 0) {
            c.d[i] += 10; c.d[i + 1]--;
        }
    }
    c.fix();
    return c;
}

bigint operator * (const bigint &a, int b) {
    bigint c;
    int carry = 0;
    for (int i = 0; i < a.len; i++) {
        int tmp = a.d[i] * b + carry;
        c.d[c.len++] = tmp % 10;
        carry = tmp / 10;
    }
    while (carry != 0) {
        c.d[c.len++] = carry % 10; carry /= 10;
    }
    return c;
}

bigint operator * (const bigint &a, const bigint &b) {
    bigint c; c.len = a.len + b.len;
    for (int i = 0; i < a.len; i++) {
        for (int j = 0; j < b.len; j++) {
            c.d[i + j] += a.d[i] * b.d[j];
        }
    }
    for (int i = 0; i < c.len - 1; i++) {
        c.d[i + 1] += c.d[i] / 10; c.d[i] %= 10;
    }
    c.fix();
    return c;
}

bigint divide(bigint a, int b, int &r) {
    bigint c;
    c.len = a.len;
    for (int i = a.len - 1; i >= 0; i--) {
        r = r * 10 + a.d[i];
        if (r < b) c.d[i] = 0;
        else {
            c.d[i] = r / b; r %= b;
        }
    }
    c.fix();
    return c;
}
void print(bigint a) {
    for (int i = a.len - 1; i >= 0; i--) {
        printf("%d",a.d[i]);
    }
    puts("");
}

int main() {
    bigint now = change("2");
    print(now);
    for (int i = 1; i <= 100; i++) {
        now = now * 2;
        print(now);
    }
    return 0;
}

完全版高精度

#include <bits/stdc++.h>
using namespace std;
constexpr int base = 1000000000;
constexpr int base_digits = 9;

struct bigint {
    // value == 0 is represented by empty z
    vector<int> z;  // digits

    // sign == 1 <==> value >= 0
    // sign == -1 <==> value < 0
    int sign;

    bigint() : sign(1) {}

    bigint(long long v) { *this = v; }

    bigint& operator=(long long v) {
        sign = v < 0 ? -1 : 1;
        v *= sign;
        z.clear();
        for (; v > 0; v = v / base) z.push_back((int)(v % base));
        return *this;
    }

    bigint(const string& s) { read(s); }

    void trim() {
        while (!z.empty() && z.back() == 0) z.pop_back();
        if (z.empty()) sign = 1;
    }

    void read(const string& s) {
        sign = 1;
        z.clear();
        int pos = 0;
        while (pos < s.size() && (s[pos] == '-' || s[pos] == '+')) {
            if (s[pos] == '-') sign = -sign;
            ++pos;
        }
        for (int i = (int)s.size() - 1; i >= pos; i -= base_digits) {
            int x = 0;
            for (int j = max(pos, i - base_digits + 1); j <= i; j++)
                x = x * 10 + s[j] - '0';
            z.push_back(x);
        }
        trim();
    }

    friend istream& operator>>(istream& stream, bigint& v) {
        string s;
        stream >> s;
        v.read(s);
        return stream;
    }

    friend ostream& operator<<(ostream& stream, const bigint& v) {
        if (v.sign == -1) stream << '-';
        stream << (v.z.empty() ? 0 : v.z.back());
        for (int i = (int)v.z.size() - 2; i >= 0; --i)
            stream << setw(base_digits) << setfill('0') << v.z[i];
        return stream;
    }

    /*以上为读入和输出高精度的必要方法*/

    long long longValue() const {
        long long res = 0;
        for (int i = (int)z.size() - 1; i >= 0; i--) res = res * base + z[i];
        return res * sign;
    }

    /*特定时候可以用来加速*/

    bigint& operator*=(int v) {
        if (v < 0) sign = -sign, v = -v;
        for (int i = 0, carry = 0; i < z.size() || carry; i++) {
            if (i == z.size()) z.push_back(0);
            long long cur = (long long)z[i] * v + carry;
            carry = (int)(cur / base);
            z[i] = (int)(cur % base);
        }
        trim();
        return *this;
    }

    bigint operator*(int v) const { return bigint(*this) *= v; }

    bigint& operator/=(int v) {
        if (v < 0) sign = -sign, v = -v;
        for (int i = (int)z.size() - 1, rem = 0; i >= 0; --i) {
            long long cur = z[i] + rem * (long long)base;
            z[i] = (int)(cur / v);
            rem = (int)(cur % v);
        }
        trim();
        return *this;
    }

    bigint operator/(int v) const { return bigint(*this) /= v; }

    int operator%(int v) const {
        if (v < 0) v = -v;
        int m = 0;
        for (int i = (int)z.size() - 1; i >= 0; --i)
            m = (int)((z[i] + m * (long long)base) % v);
        return m * sign;
    }

    /*以上为高精度和整数的乘法除法取模，没有依赖项，互相之间也不依赖*/

    bool operator<(const bigint& v) const {
        if (sign != v.sign) return sign < v.sign;
        if (z.size() != v.z.size())
            return z.size() * sign < v.z.size() * v.sign;
        for (int i = (int)z.size() - 1; i >= 0; i--)
            if (z[i] != v.z[i])
                return z[i] * sign < v.z[i] * sign;
        return false;
    }
    bool operator<=(const bigint& v) const { return !(v < *this); }

    bool operator>=(const bigint& v) const { return !(*this < v); }

    bool operator!=(const bigint& v) const { return *this < v || v < *this; }

    friend bigint operator-(bigint v) {
        if (!v.z.empty()) v.sign = -v.sign;
        return v;
    }

    bigint& operator+=(const bigint& other) {
        if (sign == other.sign) {
            for (int i = 0, carry = 0; i < other.z.size() || carry; ++i) {
                if (i == z.size()) z.push_back(0);
                z[i] += carry + (i < other.z.size() ? other.z[i] : 0);
                carry = z[i] >= base;
                if (carry) z[i] -= base;
            }
        }
        else if (other != 0 /* prevent infinite loop */) {
            *this -= -other;
        }
        return *this;
    }

    friend bigint operator+(bigint a, const bigint& b) { return a += b; }

    bigint& operator-=(const bigint& other) {
        if (sign == other.sign) {
            if ((sign == 1 && *this >= other) || (sign == -1 && *this <= other)) {
                for (int i = 0, carry = 0; i < other.z.size() || carry; ++i) {
                    z[i] -= carry + (i < other.z.size() ? other.z[i] : 0);
                    carry = z[i] < 0;
                    if (carry) z[i] += base;
                }
                trim();
            }
            else {
                *this = other - *this;
                this->sign = -this->sign;
            }
        }
        else {
            *this += -other;
        }
        return *this;
    }

    friend bigint operator-(bigint a, const bigint& b) { return a -= b; }

    /*以上为高精度加减所依赖项*/

    static vector<int> convert_base(const vector<int>& a, int old_digits, int new_digits) {
        vector<long long> p(max(old_digits, new_digits) + 1);
        p[0] = 1;
        for (int i = 1; i < p.size(); i++) p[i] = p[i - 1] * 10;
        vector<int> res;
        long long cur = 0;
        int cur_digits = 0;
        for (int v : a) {
            cur += v * p[cur_digits];
            cur_digits += old_digits;
            while (cur_digits >= new_digits) {
                res.push_back(int(cur % p[new_digits]));
                cur /= p[new_digits];
                cur_digits -= new_digits;
            }
        }
        res.push_back((int)cur);
        while (!res.empty() && res.back() == 0) res.pop_back();
        return res;
    }

    typedef vector<long long> vll;

    static vll karatsubaMultiply(const vll& a, const vll& b) {
        int n = (int)a.size();
        vll res(n + n);
        if (n <= 32) {
            for (int i = 0; i < n; i++)
                for (int j = 0; j < n; j++) res[i + j] += a[i] * b[j];
            return res;
        }

        int k = n >> 1;
        vll a1(a.begin(), a.begin() + k);
        vll a2(a.begin() + k, a.end());
        vll b1(b.begin(), b.begin() + k);
        vll b2(b.begin() + k, b.end());

        vll a1b1 = karatsubaMultiply(a1, b1);
        vll a2b2 = karatsubaMultiply(a2, b2);

        for (int i = 0; i < k; i++) a2[i] += a1[i];
        for (int i = 0; i < k; i++) b2[i] += b1[i];

        vll r = karatsubaMultiply(a2, b2);
        for (int i = 0; i < a1b1.size(); i++) r[i] -= a1b1[i];
        for (int i = 0; i < a2b2.size(); i++) r[i] -= a2b2[i];

        for (int i = 0; i < r.size(); i++) res[i + k] += r[i];
        for (int i = 0; i < a1b1.size(); i++) res[i] += a1b1[i];
        for (int i = 0; i < a2b2.size(); i++) res[i + n] += a2b2[i];
        return res;
    }

    bigint operator*(const bigint& v) const {
        vector<int> a4 = convert_base(this->z, base_digits, 4);
        vector<int> b4 = convert_base(v.z, base_digits, 4);
        vll a(a4.begin(), a4.end());
        vll b(b4.begin(), b4.end());
        while (a.size() < b.size()) a.push_back(0);
        while (b.size() < a.size()) b.push_back(0);
        while (a.size() & (a.size() - 1)) a.push_back(0), b.push_back(0);
        vll c = karatsubaMultiply(a, b);
        bigint res;
        res.sign = sign * v.sign;
        for (int i = 0, carry = 0; i < c.size(); i++) {
            long long cur = c[i] + carry;
            res.z.push_back((int)(cur % 10000));
            carry = (int)(cur / 10000);
        }
        res.z = convert_base(res.z, 4, base_digits);
        res.trim();
        return res;
    }

    bigint& operator*=(const bigint& v) {
        *this = *this * v;
        return *this;
    }

    /*以上为高精度乘法所依赖项*/

    bigint abs() const { return sign == 1 ? *this : -*this; }

    friend pair<bigint, bigint> divmod(const bigint& a1, const bigint& b1) {
        int norm = base / (b1.z.back() + 1);
        bigint a = a1.abs() * norm;
        bigint b = b1.abs() * norm;
        bigint q, r;
        q.z.resize(a.z.size());

        for (int i = (int)a.z.size() - 1; i >= 0; i--) {
            r *= base;
            r += a.z[i];
            int s1 = b.z.size() < r.z.size() ? r.z[b.z.size()] : 0;
            int s2 = b.z.size() - 1 < r.z.size() ? r.z[b.z.size() - 1] : 0;
            int d = (int)(((long long)s1 * base + s2) / b.z.back());
            r -= b * d;
            while (r < 0) r += b, --d;
            q.z[i] = d;
        }

        q.sign = a1.sign * b1.sign;
        r.sign = a1.sign;
        q.trim();
        r.trim();
        return {q, r / norm};
    }

    bigint operator/(const bigint& v) const { return divmod(*this, v).first; }

    bigint operator%(const bigint& v) const { return divmod(*this, v).second; }

    bigint& operator/=(const bigint& v) {
        *this = *this / v;
        return *this;
    }

    /*以上为高精度除法所依赖项*/

    bool operator>(const bigint& v) const { return v < *this; }

    bool operator==(const bigint& v) const {
        return !(*this < v) && !(v < *this);
    }

    /*以上为高精度快速幂所依赖项*/

    bool isZero() const { return z.empty(); }

    friend bigint gcd(const bigint& a, const bigint& b) {
        return b.isZero() ? a : gcd(b, a % b);
    }

    friend bigint lcm(const bigint& a, const bigint& b) {
        return a / gcd(a, b) * b;
    }

    /*以上为高精度gcd所依赖项*/

    friend bigint sqrt(const bigint& a1) {
        bigint a = a1;
        while (a.z.empty() || a.z.size() % 2 == 1) a.z.push_back(0);

        int n = (int)a.z.size();

        int firstDigit = (int)::sqrt((double)a.z[n - 1] * base + a.z[n - 2]);
        int norm = base / (firstDigit + 1);
        a *= norm;
        a *= norm;
        while (a.z.empty() || a.z.size() % 2 == 1) a.z.push_back(0);

        bigint r = (long long)a.z[n - 1] * base + a.z[n - 2];
        firstDigit = (int)::sqrt((double)a.z[n - 1] * base + a.z[n - 2]);
        int q = firstDigit;
        bigint res;

        for (int j = n / 2 - 1; j >= 0; j--) {
            for (;; --q) {
                bigint r1 =
                    (r - (res * 2 * base + q) * q) * base * base +
                    (j > 0 ? (long long)a.z[2 * j - 1] * base + a.z[2 * j - 2] : 0);
                if (r1 >= 0) {
                    r = r1;
                    break;
                }
            }
            res *= base;
            res += q;

            if (j > 0) {
                int d1 = res.z.size() + 2 < r.z.size() ? r.z[res.z.size() + 2] : 0;
                int d2 = res.z.size() + 1 < r.z.size() ? r.z[res.z.size() + 1] : 0;
                int d3 = res.z.size() < r.z.size() ? r.z[res.z.size()] : 0;
                q = (int)(((long long)d1 * base * base + (long long)d2 * base + d3) / (firstDigit * 2));
            }
        }

        res.trim();
        return res / norm;
    }
};

bigint fpow (bigint a, bigint b) {
    bigint res = 1;
    while (b > 0) {
        if (b % 2 == 1) res *= a;
        a *= a;
        b /= 2;
    }
    return res;
}

bigint a, b, c;

int main()
{
    cin >> a >> b;
    long long x = 1000000000000;
    cout << a * b << endl;
    cout << a - x << endl;
    return 0;
}