How does the below program output `C89` when compiled in C89 mode and `C99` when compiled in C99 mode?

How does the below program output `C89` when compiled in C89 mode and `C99` when compiled in C99 mode?

c printf comments c99 c89

c

Remove comments from C/C++ code

c++ c comments

c

Does the C preprocessor strip comments or expand macros first? [duplicate]

c comments c-preprocessor c99

c

Remove C and C++ comments using Python?

c++ python c regex comments

c

Where to document functions in C or C++? [closed]

c documentation comments header-files

c

How do I enable C++ styled comments in gcc while leaving ANSI enabled?

c++ c gcc comments

c