QUIZ 8

1. Describe the concepts virtual functions and dynamic binding.
   • Virtual Functions
     • Typically, pointer-class determines functions
     • virtual functions; object (not pointer) determines function called
     • Program determines proper (say draw) function at run time (dynamically)
     • Treat all shapes generically
     • Declare draw as virtual in base class
     • Override draw in each derived class; like redefining, but new function must have same signature
     • Once declared virtual, virtual in all derived classes; good practice to explicitly declare virtual
   • Dynamic binding
     • Choose proper function to call at run time
     • Only occurs off pointer handles; if function called from object, uses that object"s definition
     • Base-class pointer to derived-class object; will call derived-class function
2. Decsribe the concepts abstract class and concrete class.
   • Abstract classes
     • Sole purpose: to be a base class (called abstract base classes)
     • Incomplete; derived classes fill in ``missing pieces''
     • Cannot make objects from abstract class; however, can have pointers and references
     • Abstract classes not required, but helpful
     • To make a class abstract, Need one or more ``pure'' virtual functions
     • Regular virtual functions; have implementations, overriding is optional
     • Pure virtual functions; no implementation, must be overridden
   • Concrete classes
     • Can instantiate objects
     • Implement all functions they define
     • Provide specifics