PAT 甲级 1001 A+B Format

题目链接：https://pintia.cn/problem-sets/994805342720868352/problems/994805528788582400

题意

给出两个数，将二者的和从个位起以三位为间隔输出。

代码

#include <bits/stdc++.h>
using namespace std;
int main() {
    int a, b; cin >> a >> b;
    string s = to_string(a + b);
    int cnt = 0;
    for (int i = s.size() - 1; i >= 0; i--) {
        if (++cnt % 3 == 0) {
            if (i - 1 >= 0 and isdigit(s[i - 1])) {
                s.insert(i, ",");
            }
        }
    }
    cout << s << "\n";
}