value assigned to a property in the model class disappears in the view/controller class

Question

Right before my model class sends the variable stringToDisplay, NSLog shows me that it has a value. But when I try to use it in my ViewController, I just get

Answer 1

Oh - your declaration of the property whatHappenedSinceLastClear isn't exposed to other classes that import CalculatorBrain.h because you put the property declaration in an interface extension in the .m file, which other classes will not see.

To make it publicly accessible move the @property line for whatHappenedSinceLastClear to CalculatorBrain.h, not the .m file.