知识点：字符串处理、数字拆分处理、模拟

法1）数字拆分处理 + 模拟

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
string s, res;
string c[10] = {"zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine"};
int num, t;
int main() {
    cin >> s;
    for (int i = 0; s[i]; i ++ ) num += s[i] - '0';
    if(!num) res = c[0];
    while (num) {
        if(t) res = ' ' + res;
        res = c[num % 10] + res;
        num /= 10;
        t ++;
    }
    cout << res << endl;
    return 0;
}

字符串处理 + 模拟(看了y总的写法后写的，确实比原来的代码简化了，容易了)

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
string s, res;
string c[10] = {"zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine"};
int num, t;
int main() {
    cin >> s;
    for (auto x : s) num += x - '0';
    res = to_string(num);
    for (int i = 0; res[i]; i ++ ) {
        cout << c[res[i] - '0'];
        if(res[i + 1]) cout << ' ';
        else cout << endl;
    }
    return 0;
}