参考

#include <iostream>
using namespace std;

int main () {

    unsigned long long a, b;
    cin >> a >> b;
    int stack[24], si = 0, c = 0;
    while (a > 0 || b > 0) {
        int t = a % 10 + b % 10 + c;
        c = t / 10;
        stack[++si] = t % 10;
        a /= 10, b /= 10;
    }
    if (c != 0) stack[++si] = 1;
    for (int i = si; i >= 1; i --) cout << stack[i];
    cout << endl;

    return 0;
}