testSelect.cc   :  conditional compilation
testMacro.cc    :  simple preprocessor macros
absPitFall.cc   :  pitfall with macro computing abs value

to compile:
c++ -Wall -o testMacro   testMacro.cc
c++ -Wall -o testSelect  testSelect.cc
c++ -Wall -o absPitFall  absPitFall.cc
