基础高精度算法：高精度四则运算

#if 1
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

vector<int> add(vector<int> A, vector<int> B) {
    vector<int> C;

    int t = 0;
    for (int i = 0; i < A.size() || i < B.size(); i++) { 
        if (i < A.size()) t += A[i]; 
        if (i < B.size()) t += B[i];
        
        C.push_back(t % 10);
        t /= 10;
    }

    if (t) C.push_back(1);
    
    return C;
}

//非负的A>=B，返回true
//A、B均为逆序存储
bool cmp(vector<int>& A, vector<int>& B) {
    if (A.size() != B.size()) return A.size() > B.size();
    for (int i = A.size() - 1; i >= 0; i--) {
        if (A[i] != B[i]) return A[i] >= B[i];
    }
    return true;
}

vector<int> sub(vector<int>& A, vector<int>& B) {
    vector<int> D;

    for (int i = 0, t = 0; i < A.size() || i < B.size(); i++) {
        t = A[i] - t;
        if (i < B.size()) t -= B[i];
        
        D.push_back((t + 10) % 10);
        
        if (t >= 0) t = 0;
        else t = 1;
    }

    while (D.size() > 1 && D.back() == 0) D.pop_back();

    return D;
}

vector<int> mul(vector<int>& A, int b) {
    vector<int> E;
    
    for (int i = 0, t = 0; i < A.size() || t; i++) {
        if(i < A.size()) t += A[i] * b;
        
        E.push_back(t % 10);
        t /= 10;
    }
    
    return E;
}

vector<int> div(vector<int>& A, int b, int& r) {
    vector<int> F;
    
    r = 0;
    for (int i = A.size() - 1; i >= 0; i--) {
        r = r * 10 + A[i];
        
        F.push_back(r / b);
        r %= b;
    }

    reverse(F.begin(), F.end());
    while (F.size() > 1 && F.back() == 0) F.pop_back();

    return F;
}

int main() {
    string a, b; //"123456"
    cin >> a >> b;
    
    vector<int> A, B;
    for (int i = a.size() - 1; i >= 0; i--) A.push_back(a[i] - '0'); //[6,5,4,3,2,1]
    for (int i = b.size() - 1; i >= 0; i--) B.push_back(b[i] - '0');
    
    vector<int> C = add(A, B);
    for (int i = C.size() - 1; i >= 0; i--) printf("%d", C[i]);
    
    cout << endl;
    
    if (cmp(A, B)) {
        auto D = sub(A, B);
        for (int i = D.size() - 1; i >= 0; i--) printf("%d", D[i]);
    }
    else {
        auto D = sub(B, A);
        printf("-");
        for (int i = D.size() - 1; i >= 0; i--) printf("%d", D[i]);
    }

    cout << endl;
    
    int c;
    scanf("%d", &c);
    
    auto E = mul(A, c);
    for (int i = E.size() - 1; i >= 0; i--) printf("%d", E[i]);

    cout << endl;
    
    int r;
    auto F = div(A, c, r);

    for (int i = F.size() - 1; i >= 0; i--) printf("%d", F[i]);
    printf("...%d", r);
    
    
    return 0;
}
#endif