7.高精度加法

#include <bits/stdc++.h>
using namespace std;
vector<int> add(vector<int> &A, vector<int> &B) { //加上引用，不然很慢 
    vector<int> C; //答案 
    int t = 0; //进位 
    for (int i = 0; i < A.size() || i < B.size(); i++) {
        //让t来表示三个数的和 
        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;
}
int main() {
    string a, b; //太长了，所以用字符串来读入 
    cin >> a >> b;
    vector<int> A, B; //然后存进vector 
    for (int i = a.length() - 1; i >= 0; i--) {
        A.push_back(a[i] - '0'); //字符变数字 
    }
    for (int i = b.length() - 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--) {
        cout << C[i];
    }
    return 0;
}

2020年9月29日更新： 高精度压位压8位的做法

#include <bits/stdc++.h>
using namespace std;
const int base = 100000000;
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 % base);
        t /= base;
    }
    if (t) {
        C.push_back(t);
    }
    return C;
}
int main() {
    string a, b;
    cin >> a >> b;
    vector<int> A, B, C;
    for (int i = a.size() - 1, s = 0, j = 0, t = 1; i >= 0; i--) {
        s += (a[i] - '0') * t;
        j++;
        t *= 10;
        if (j == 8 || i == 0) {
            A.push_back(s);
            s = 0;
            j = 0;
            t = 1;
        }
    }
    for (int i = b.size() - 1, s = 0, j = 0, t = 1; i >= 0; i--) {
        s += (b[i] - '0') * t;
        j++;
        t *= 10;
        if (j == 8 || i == 0) {
            B.push_back(s);
            s = 0; 
            j = 0;
            t = 1;
        }
    }
    C = add(A, B);
    cout << C.back();
    for (int i = C.size() - 2; i >= 0; i--) {
        printf("%08d", C[i]);
    }
    return 0;
}