Control Flow Workbook

Practice problems for Kotlin’s if Returns a Value, So There’s No Ternary. 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.

if as an expression

1. Assign from an if

Given score, assign grade the value "pass" when score > 50, otherwise "fail".

val grade = if (score > 50) "pass" else "fail"

2. No ternary needed

Rewrite the Java expression x > 0 ? "+" : "-" in Kotlin.

if (x > 0) "+" else "-"

Ranges

3. Two ranges

Write a range covering 1 through 10 inclusive, and one covering 1 through 9 (excluding the upper end).

1..10
1 until 10

4. Count down

Print 5, 4, 3, 2, 1 with a single for loop.

for (i in 5 downTo 1) println(i)

5. Every other number

Print 0, 2, 4, 6, 8, 10 with a single for loop.

for (i in 0..10 step 2) println(i)

6. A range membership check

Write a condition that is true when age is between 18 and 65, both inclusive.

age in 18..65

for, indices, and in

7. Walk the elements

Given a list names, print each name. No index.

for (name in names) println(name)

8. Index and value together

Print each name in names prefixed by its index, e.g. 0: Ada.

for ((i, name) in names.withIndex()) {
    println("$i: $name")
}

9. Loop over positions

Print the indices of names (0, 1, 2, …) using the list’s own index range.

for (i in names.indices) println(i)

10. Not a member

Given a list valid, write a condition that’s true when command is not in it.

command !in valid

11. Break out of both loops

Given a grid of rows of cells, break out of both loops the moment you hit a cell where isMine is true.

outer@ for (row in grid) {
    for (cell in row) {
        if (cell.isMine) break@outer
    }
}

Back to the lesson, Kotlin’s if Returns a Value, or on to the next one: when.