Convert numbers to words

Over the course of my career, I've used a lot of programming languages. When learning a new language, I like to have a project to work on that exposes me to the nuances of the language. The numwords class is one of my favorite exercises for this purpose. I have written it in dozens of languages over the years, including several times in C and C++.

numwords is a class that spells out a number in words. It can be useful for banking and accounting applications. It looks like this in use:

int main() {
    bw::numword nw{};
    uint64_t n;
    nw = 3; bw::print("n is {}, {}\n", nw.getnum(), nw);
    nw = 47; bw::print("n is {}, {}\n", nw.getnum(), nw);
    n = 100073; bw::print("n is {}, {}\n", n, 
      bw::numword{n});
    n = 1000000001; bw::print("n is {}, {}\n&quot...