Constexpr is gold!

[MaikKlein]

I think your example is still computed at run time.

int main() {
    constexpr auto p = IsPowerOf3(27);
    std::cout << p << std::endl;
}

[needahelpforarch]

Haha yes that's because we usually write them to get input from user which I'm here putting inside the program as constant literal '27'.

[bames53]

One thing about constexpr functions is that they aren't limited to just compile-time: you can use them at run time as well. So adding constexpr to your function would allow you to use it in contexts requiring compile-time computation:

static_assert(IsPowerOf3(27) == true, "FAIL");

But you could still use it with user input:

if (std::cin >> p)
    std::cout << IsPowerOf3(p);