Do I have to use #include beside ?

Question

I started learning C++ and I read a book which writes that I must use the header file because the string type is not built directly into the comp

Answer 1

Yes, you have to include what you use. It's not mandated that standard headers include one another (with a few exceptions IIRC). It might work now, but might fail on a different compiler.

In your case, apparently includes , directly or indirectly, but don't rely on it.