If a class has one or more secondary constructors, what must each of them do?

When you can omit constructor keyword from the primary constructor?

How many different kinds of constructors are available for kotlin classes?

What is the default visibility modifier in Kotlin?

You are writing a console app in Kotlin that processes test entered by the user. If the user enters an empty string, the program exits. Which kind of loop would work best for this app? Keep in mind that the loop is entered at least once

What is the entry point for a Kotlin application?

Inside an extension function, what is the name of the variable that corresponds to the receiver object

Kotlin interfaces and abstract classes are very similar. What is one thing abstract class can do that interfaces cannot?