Compile-time func

#include <array>
#include <iostream>
#include <exception>

constexpr int requires_positive(int num) {
    return (num <= 0) ? throw std::exception() : num;
}

constexpr int factorial(int num) {
    return (num > 1) ? num * factorial(num - 1) : 1;
}

constexpr int arrangement(int k, int n) {
    return requires_positive(k),
           requires_positive(n),
           factorial(n) / factorial(n - k);
}

int main(int argc, char** argv) {
    //demonstration
    std::array<char, arrangement(1, 2)> good_array;
    //error demonstration
    std::array<char, arrangement(0, 1)> bad_array_1;
    //one more error demonstration
    std::array<char, arrangement(-1, 1)> bad_array_2;

    return 0;
}