7.1 Interacting with C and Objective-C APIs7.1.1 Optional Properties and Return Values7.1.2 AnyObject Types7.1.3 Subclassing, Extensions, and Protocols7.1.4 Automatically Converted Types7.1.5 Selectors and Enums7.1.6 Working with C Code7.2 Working with Swift and Objective-C in a Single ProjectExercises