Answer 1

Try to place #include "stdafx.h" above #include <iostream>

Answer 2

You seem to be using Visual Studio, and if that is the case, you may need to include the <string> header for string functionalities btw. After scavenging the net, this should fix your problem:

In Visual Studio you must #include "stdafx.h" and be the first include of the cpp file

This is weird. The problem doesn't exist on VS 2017.