fix a compile error in a code example

[estshorter]

not keyword is not defined in C++ and the code example causes a compile error.
This PR fixes the issue above.

[ToruNiina]

Actually, not is a keyword in C++ and should be available without doing anything. (in C, it is not a keyword but a valid identifier.) MSVC does not define it because of some reasons, but it, strictly speaking, violates C++ standard.

But anyway, many people uses MSVC and example should be compatible with as many environment as possible, so okay I will merge this.

[estshorter]

I didn't know the alternative operators.
Thank you for letting me know!