Question

I stumble upon some C++ code like this:

int $T$S;

First I thought that it was some sort of PHP code or something wrongly pasted in there, but it compiles and runs nicely (on MSVC 2008).

What kind of characters are valid for variables in C++ and are there other weird characters you can use?

Answer 1

The only legal characters according to the standard are alphanumerics
and the underscore. The standard does require that just about anything
Unicode considers alphabetic is acceptable (but only as single
code-point characters). In practice, implementations offer extensions
(i.e. some do accept a $) and restrictions (most don’t accept all of the
required Unicode characters). If you want your code to be portable,
restrict symbols to the 26 unaccented letters, upper or lower case, the
ten digits, and the ‘_’.