全WA，求带！

#include <iostream>

std::string add(std::string First, std::string Second) {
    int na = First.size(), nb = Second.size();
    int nas = na > nb ? na : nb;
    int a[nas + 1], b[nas + 1];
    for (int i = 1; i <= na; i++) a[i] = First[na - i] - '0';
    for (int i = 1; i <= nb; i++) b[i] = Second[nb - i] - '0';
    for (int i = 1; i <= nas; i++) {
        a[i] = a[i] + b[i];
        if (a[i] > 9) a[i + 1] += 1, a[i] -= 10;
    }
    if (!a[nas]) nas += 1;
    std::string ans = "";
    while (nas --> 0) ans += a[nas] + '0';
    return ans;
}

int main() {
    std::string a, b;
    std::cin >> a >> b;
    std::cout << add(a, b);
    return 0;
}