Focus would be given to the user interface, user friendliness, overall functionality, as well as organization and structure.

Software testing can be done either through black box testing or white box testing.

A class can contain default implementation, while an interface should not contain any implementation at all.

YES, structures do support inheritance

All declarations inside a structure are by default public, while all members inside a class are private

Encapsulation, oftentimes associated with information hiding, reduces software development risk by shifting the code's dependency on an uncertain implementation onto a well-defined interface.

Polymorphism is the ability of objects belonging to different types to respond to method calls of the same name, each one according to an appropriate type-specific behavior. It means that if class B inherits from class A, it doesn't have to inherit everything about class A. That is, it can do some of the things that class A does differently.