When you compile with /Za (Microsoft extensions disabled), the compiler generates a warning if two macros are the same except for the spelling of a macro argument. The C 7.0 compiler generates a warning when it encounters the second macro in this example:
#define findnum( a ) a
#define findnum( b ) b
Version 6.0 of the Microsoft C compiler did not generate a warning in this case. The macro expansion is the same.