（枚举因数）从小到大打印正整数 $n$ 的所有正因数。

试补全枚举程序。

1#include <bits/stdc++.h>2using namespace std;3 4int main(){5    int n;6    cin >> n;7 8    vector<int> fac;9    fac.reserve((int)ceil(sqrt(n)));10 11    int i;12    for (i = 1; i * i < n; ++i){13        if (①){14            fac.push_back(i);15        }16    }17 18    for (int k = 0; k < fac.size(); ++k){19        cout << ② << "";20    }21    if (③) {22        cout << ④ << "";23    }24    for (int k = fac.size() - 1; k >= 0; --k){25        cout << ⑤ << "";26    }27}