I haven’t done much low level stuff, but I think the ‘main’ function is something the compiler uses to establish an entry point for the compiled binary. The name ‘main’ would not exist in the compiled binary at all, but the function itself would still exist. Executable formats aren’t all the same, so they’ll have different ways of determining where this entry point function is expected to be. You can ‘run’ a binary library file by invoking a function contained therein, which is how DLL files work.

Yeah, he was bamboozled as soon as he agreed to allow multiple separate files. The challenge was bs from the start, but he could have at least nailed it down with more explicit language and by forbidding any exceptions. I think it’s kind of ironic that the instructions for a challenge related to different representations of information failed themselves to actually convey the intended information.