Methods and instance variables are declared in the header file (in this case, QuizViewController.h), but the actual code for the methods is placed in the implementation file (in this case, QuizViewController.m). Select QuizViewController.m in the project navigator.
When you create a new application in Xcode, the template fills in a lot of boiler-plate code. This code may be useful for you later on, but for now, it is distracting. So we’re going to remove it. In QuizViewController.m, delete everything between the @implementation and @end directives so that QuizViewController.m looks like this:
@implementation QuizViewController @end
When the application launches, the QuizViewController ...