lst-0016-book.cpp
// https://godbolt.org/z/zfe7dM4ex
#include <array>
#include <iostream>
constexpr size_t MONTHS = 12; /* months in year */
int main() {
std::array<unsigned,MONTHS> mdays = { // okay with a constant
31,28,31,30,31,30,31,31,30,31,30,30,30,31};
unsigned age = 0;
std::cout << "How old are you? "; std::cin >> age;
std::array<int,age> years of life; // (ERR) array size not by variable
}