加法

#include<algorithm>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<vector>
using namespace std;
vector<int> add(vector<int> &A,vector<int> &B)
{
    if(A.size()<B.size())return add(B,A);

    vector<int>c;
    int t=0;
    for(int i=0;i<A.size();i++)
    {
        t +=A[i];
        if(i<B.size())t+=B[i];
        c.push_back(t%10);
        t/=10;

    }
    if(t)c.push_back(t);
    return c;
}

int main()
{
    string a,b;
    vector<int>A,B;
    cin>>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;




}

减法

#include<bits/stdc++.h>
using namespace std;
vector<int> sub(vector<int> &A,vector<int>&B)
{
    vector<int>c;
    int t=0;
    if(A.size()<B.size())return sub(B,A);
    for(int i=0;i<A.size();i++)
    {
        t=A[i]+t;
        if(i<B.size())t -=B[i];
        c.push_back((t+10)%10);
        if(t<0)t=1;
        else t = 0;
    }
    while(c.size()>1 and c.back()==0)c.pop_back();
    return c;
}



int main()
{
    string a,b;
    vector<int>A,B;
    cin>>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 = sub(A,B);

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

    return 0;
}