I have 'C' code that was written in 1985 that runs today, mostly after moving function parameters from inside the function to inside the argument list.

'C' seems to be a language that makes it easy to write incomprehensible statements, but it's not that hard (or it was not that hard) to write code that is trivial bring up to date. Perhaps it was easier for me because I started with Fortran.

Very common.