I give you `if (0 > fdprintf (STDERR_FILENO, ...))` instead. But on a serious matter, it's a good thing to tell a beginner that diagnostics belong on stderr, n

I give you `if (0 > fdprintf (STDERR_FILENO, ...))` instead. But on a serious matter, it's a good thing to tell a beginner that diagnostics belong on stderr, not stdout.