I was talking to a friend about C++ and I thought "Man, C++ shit from last year won't compile this year, I'm certain my first C program still runs...Actually, maybe it goes back even farther" and it does.

So, a C program from 1979 still compiles and runs in 2021. That's pretty fuckin' cool. Some other stuff from V7 Unix doesn't, like sed doesn't build for a few reasons, but check it out:
warnings_because_headers_have_changed_but_it_still_works.png