You need to do one of two things:
- Declare the array to be a fixed size (probably not what you want)
- Make it a pointer. But then you need to properly
malloc
andfree
the array as needed.
A better choice is to not use a struct
and instead create a full class. Then you can add methods and properties as well as make memory management much easier. You are working in Objective-C. Take advantage of the Object Oriented aspects of the language. Add a method to calculate the circumference and area, etc. Put the logic where it belongs.