加法

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

vector <int> add(vector<int> &A,vector<int> &B)
{
    vector<int> C;
    int t = 0;//表示进位
    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!=0) C.push_back(1);
    return C;
}

int main()
{
    string a, b;
    cin >> a >> b;//输入123456789
    vector <int> A,B;
    for (int i = a.size() - 1; i >= 0; i -- ) A.push_back(a[i] - '0');
    for (int i = b.size() - 1; i >= 0; i -- ) B.push_back(b[i] - '0');

    auto c=add(A,B);

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

除法

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;

vector<int> div(vector<int> &A, int B, int &r)
{
    vector<int> C;
    for (int i = 0; i < A.size(); i ++ )
    {
        r = r * 10 + A[i];
        C.push_back(r/B);
        r = r % B;
    }
    reverse(C.begin(), C.end());
    while(C.size() > 1 && C.back() == 0)//去除前导0
        C.pop_back();
    return C;
}

int main()
{
    string a;
    vector<int> A;

    int B;
    cin >> a >> B;
    for (int i = 0; i < a.size(); i ++ )
        A.push_back(a[i] - '0');
    int r = 0;//余数
    auto C = div(A, B, r);

    reverse(C.begin(), C.end());
    for (int i = 0; i < C.size(); i ++ )
        cout << C[i];
    cout << endl << r;
    return 0;
}