The syntax for a symbol name is:
{ letter | _ | $ | . } { letter | _ | $ | . | digit }* In the above syntax:
Uppercase and lowercase letters are distinct; the underscore ( _ ), dollar sign ($), and dot ( . ) are treated as alphabetic characters.
Symbol names that begin with a dot ( . ) are assumed to be local symbols. To simplify debugging, avoid using this type of symbol name in hand-coded assembly language routines.
The symbol dot ( . ) is predefined and always refers to the address of the beginning of the current assembly language statement.
External variable names beginning with the underscore character are reserved by the ANSI C Standard. Do not begin these names with the underscore; otherwise, the program will not conform to ANSI C and unpredictable behavior may result.