why do i need to include to use them?

Question

I am new to C++ and trying to figure out how to use vector.

More specifically, I want to know when I need to use #include. I

Answer 1

You may see code that does not #include directly. But if you inspect the preprocessed code I'm certain you'll find that that code did include the header - but indirectly through some other header.

This is fragile and you shouldn't do it. But that doesn't mean it does not work.