560#import vs #include in Objective C – A quick reminder

#import is identical to #include, except that it makes sure that the same file is never included more than once. It’s therefore preferred and is used in place of #include in code examples throughout Objective-C–based documentation.
http://developer.apple.com/ mac/library/documentation/ cocoa/conceptual/ObjectiveC /Articles/ ocDefiningClasses.html

76Header Search Paths

Search for “Header Search Paths” in Project Info, and add the path to your headers. (MacPorts headers live in /opt/local/include) Also: #include is for System Header files. #include "display.h" is for User Header files