Data Types Workbook

Practice problems for In Kotlin, There Are No Primitives. Each takes a minute or two. Write your own answer first, then click Show answer — nothing here is a trick question, just direct practice of the syntax from the lesson.

val, var, and the number types

1. Read-only and mutable

Declare a read-only name holding "Ada" and a mutable age holding 36, then reassign age to 37.

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val name = "Ada"
var age = 36
age = 37

2. Literals pick their type

Write literals for: a Long equal to 42, a Double equal to 3.14, and a Float equal to 3.14.

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val l = 42L
val d = 3.14
val f = 3.14f

3. A readable big number

Write the literal 8100000000 as a Long with digit separators for readability.

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val population = 8_100_000_000L

4. No implicit widening

This doesn’t compile: val l: Long = anInt. Fix it without changing anInt’s type.

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val l: Long = anInt.toLong()

Kotlin never widens numeric types silently — you convert explicitly.

Char, strings, and templates

5. A character’s code

Given val grade: Char = 'A', get its numeric code (65).

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grade.code

Char is its own type, not a number, so you ask for the code rather than using it as one.

6. A string template

Given val age = 36, print Next year: 37 using a string template with an expression.

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println("Next year: ${age + 1}")

7. A raw string

Write the Windows path C:\Users\ada as a string literal without escaping the backslashes.

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val path = """C:\Users\ada"""

Nullability and the special types

8. Opt into null

Declare a String that may hold null and assign it null. Then declare one that may not hold null.

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var maybe: String? = null
val name: String = "Ada"

9. Length or zero

Given val maybe: String?, produce its length, or 0 when it’s null, in one expression.

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maybe?.length ?: 0

10. A function that never returns

Write fail(message: String) that always throws IllegalStateException. What’s its return type?

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fun fail(message: String): Nothing = throw IllegalStateException(message)

Nothing — the type of an expression that never returns a value.

11. The void stand-in

A function prints a line and returns no meaningful value. What is its return type, and do you have to write it?

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The return type is Unit, and you don’t write it — it’s the default when you omit the return type.

fun log(msg: String) {
    println(msg)
}

Back to the lesson, In Kotlin, There Are No Primitives, or on to the next one: functions.

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