finish exercise1 for chapter4
Merge branch 'master' of https://github.com/qiaoyuguo/practice
copy AirportCodes.cpp from textbook
copy cctype.cpp and cctype.h from textbook(just a interface, so no
Makefile)
copy TwoLetterWords.cpp from textbook
finish exercise3 for chapter5
finish exercise4 for chapter5
finish exercise5 for chapter5
finish exercise8 for chapter5
finish exercise12 for chapter5