高精度加减乘除

//存储数据
int main()
{
    string 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');

}

加法

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

    int t = 0;//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)  C.push_back(1);

    return C;
}

减法

//判断A与B的大小
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;
    int t = 0;

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

        //判断是否借位
        if(t < 0) t = 1;
        else t = 0;
    }

    //去除前导0
    while(C.size() > 1 && C.back() == 0)  C.pop_back();

    return C;
}

乘法

vector<int> mul(vector<int> &A, int b)
{
    vector<int> C;

    int t = 0;
    for(int i = 0; i < A.size() || t != 0; i ++ )
    {
        if(i < A.size()) t += A[i] * b;
        C.push_back(t % 10);

        t /= 10;
    }
    return C;

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

除法

vector<int> div(vector<int> &A, int b, int &r)//除数，被除数和余数
{
    vector<int> C;

    int r = 0;

    //除法从高位开始操作
    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() > 0 && C.back() == 0) C.pop_back();

    return C;
}