#Warning with variables

the #warning tag is a preprocessor directive. This means that it is processed by the compiler before the main code. It's only around when compiling, a time at which any variable definitely won't have a value yet, so it would not make any sense for it to be able to interact with variables.

I guess it could technically interact with constants, but again, those will have been read after the preprocessor directives has been handled. So the answer is, again, no. Although since a constant is... constant, you could just write it out in the #warning