高精度

加法

#include <bits/stdc++.h>

using namespace std;

vector<int> add(vector<int> &A,vector<int> &B){
    vector<int> C;
    
    if (A.size()<B.size()) return add(B,A);
    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--) cout<<C[i];
    return 0;
} 

 减法

#include <iostream>
#include <vector>

using namespace std;
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> C;
    for(int i=0,t=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 && 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');
    
    vector<int> C;
    
    if(cmp(A,B)) C=sub(A,B);
    else C=sub(B,A),cout<<'-';
    
    for(int i=C.size()-1;i>=0;i--) cout<<C[i];
    return 0;
}

 乘法

#include<iostream>
#include<vector>

using namespace std;
vector<int> mul(vector<int> &A,int b)
{
    vector<int> C;
    
    int t=0;
    for(int i=0;i<A.size() || t;i++)
    {
        if(i<A.size()) t+=A[i]*b;
        C.push_back(t%10);
        t/=10;
    }
    
    while(C.size()>1 && C.back()==0) C.pop_back();
    return C;
}

int main()
{
    string a;
    int b;
    
    cin>>a>>b;
    
    vector<int>A;
    for (int i=a.size()-1;i>=0;i--) A.push_back(a[i]-'0');
    auto C=mul(A,b);
    
    for (int i=C.size()-1;i>=0;i--) cout<<C[i];
    return 0;
}

除法

#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;
vector<int> div(vector<int> &A,int b,int &r)
{
    vector<int> C;
    r=0;
    for(int i=A.size()-1;i>=0;i--)
    {
        r=r*10+A[i];
        C.push_back(r/b);
        r%=b;
    }
    reverse(C.begin(),C.end());
    while(C.size()>1 && C.back()==0) C.pop_back();
    return C;
}
int main()
{
    string a;
    vector<int> A;
    
    int B;
    cin>>a>>B;
    for(int i=a.size()-1;i>=0;i--) A.push_back(a[i]-'0');
    int r;
    auto C=div(A,B,r);
    for (int i=C.size()-1;i>=0;i--) cout<<C[i];
    cout<<endl<<r;
    
    return 0;
}