Challenge 1: A const Reference Parameter — Possible Solution
====================================================================

#include <iostream>
#include <string>

void print_length(const std::string &s) {
    std::cout << s.length() << std::endl;
}

int main() {
    print_length("Hello, world!");
    return 0;
}

Output:

    13

WHY THIS WORKS AS AN ANSWER
------------------------------
print_length takes its parameter as const std::string&, so no copy of
the string is ever made when it's called -- the function operates
directly on a reference to the temporary string constructed from the
literal. No copy-related side effects (like an extra constructor call)
are needed to make this work, exactly matching the chapter's own claim
that const reference is the idiomatic, no-copy default for passing
nontrivial types into a function.