Things I should have known about CS: Function Prototypes in C++

For your perusal at leisure

I was doing my nightly C++ review on the Programiz app. I'm not super far along, so a lot of it is super basic Intro CS stuff. 

But I actually didn't know about function prototypes. Like, at the time of writing I can't necessarily think of a time in which I would use them, but it's a cool thing to know. 

It is interesting to me how programming languages differ in terms of where you actually have to do your function declarations.