QAQ高精度模板笔记√

#include <cmath>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

const int Bit = 1000000000;
const int Max_N = 20010;

struct BigNumber {
    long long num[Max_N];
    int len;
    
    BigNumber () {
        len = 0;
        memset(num, 0, sizeof num);
    }

    BigNumber (long long A) {
        len = 0;
        while (A) {
            num[++ len] = A % Bit;
            A /= Bit;
        }
    }

    void Clear() {
        len = 0;
        memset(num, 0, sizeof num);
    }

    BigNumber operator = (const BigNumber &A) const {
        BigNumber ret;
        ret.len = A.len;
        for (int i = 1; i <= A.len; ++ i) {
            ret.num[i] = A.num[i];
        }
        return ret;
    }

    BigNumber operator + (const BigNumber &A) const {
        BigNumber ret;
        ret.len = max(A.len, len) + 3;
        for (int i = 1; i <= len; ++ i) {
            ret.num[i + 1] += (A.num[i] + num[i]) / Bit;
            ret.num[i] += (A.num[i] + num[i]) % Bit;
        }
        while (!ret.num[ret.len] && ret.len) -- ret.len;
        return ret;
    }

    BigNumber operator - (const BigNumber &A) const {
        BigNumber ret = *this;
        ret.len = max(len, A.len) + 2;
        for (int i = 1; i <= A.len; ++ i) {
            ret.num[i] -= A.num[i];
            if (ret.num[i] < 0) {
                ret.num[i] += Bit;
                ret.num[i + 1] --;
            }
        }
        while (!ret.num[ret.len] && ret.len) -- ret.len;
        return ret;
    }

    BigNumber operator * (const BigNumber &A) const {
        BigNumber ret;
        ret.len = len + A.len + 3;
        for (int i = 1; i <= len; ++ i) {
            for (int j = 1; j <= A.len; ++ j) {
                long long v = 1LL * num[i] * A.num[j] + ret.num[i + j - 1];
                ret.num[i + j] += v / Bit;
                ret.num[i + j - 1] += v % Bit;
            }
        }
        while (!ret.num[ret.len] && ret.len) -- ret.len;
        return ret;
    }

    BigNumber operator / (const int &A) const {
        BigNumber ret;
        ret.len = len + 3;
        for (int i = ret.len; i > 0; -- i) {
            ret.num[i - 1] = (ret.num[i] + num[i]) % A * Bit;
            ret.num[i] = (ret.num[i] + num[i]) / A;
        }
        ret.num[0] = 0;
        while (!ret.num[ret.len] && ret.len) -- ret.len;
        return ret;
    }

    void Read() {
        Clear();
        static char S[1000010];
        scanf("%s", S + 1);
        int N = strlen(S + 1);
        long long Pow = 1;
        for (int i = N; i; -- i) {
            if (Pow == 1) ++ len;
            num[len] += (S[i] - '0') * Pow;
            Pow *= 10;
            if (Pow == Bit) Pow = 1;
        }
    }

    void Write() {
        printf("%lld", num[len]);
        for (int i = len - 1; i > 0; -- i) {
            printf("%09lld", num[i]);
        }
    }
} ;

namespace WorkSpace {
    void Main() {
        BigNumber A;
        A.Read();
        long long B;
        scanf("%lld", &B);
        BigNumber(B).Write(); puts("");
        (A * BigNumber(B)).Write();
        return ;
    }
}

int main() {
    WorkSpace :: Main();
    return 0;
}

　　　　　　——QAQ%%%yjl