Programming in Objective-C, Sixth Edition

Class and Instance Methods

You have to define methods to work with your Fractions. You need to be able to set the value of a fraction to a particular value. Because you won’t have direct access to the internal representation of a fraction (in other words, direct access to its instance variables), you must write methods to set the numerator and denominator. You’ll also write a method called print that will display the value of a fraction. Here’s what the declaration for the print method looks like in the interface file:

-(void) print;

The leading minus sign (-) tells the Objective-C compiler that the method is an instance method. The only other option is a plus sign (+), which indicates a class method. A class method is one that performs some ...