Conditional Statements - if and when

So far the programs we have written all turn out pretty much the same. So no matter what the input we got the same output.


val score = 94.03
var grade = ""
if (score > 90) {
    grade = "A"
} else if (score > 80) {
    grade = "B"
} else {
    grade = "C"
println(grade) // => A

Or the shorthand that fits on a line for just assignment.

// or shorthand for just assignment
val score = 78.46
val quickGrade = if (score > 90) "A" else if (score > 80) "B" else "C"

Note as a block else is optional but when it’s being used as an expression (ex. the quickGrade assignment above) then else has to be there.

Collections and Ranges

With collections we can use in to check if something exists and !in to see if it does not. In the case of maps by default it checks the keys and if you want to check with values use in mapName.values

val jvmLanguages = listOf("Java", "Kotlin", "Scala", "Clojure")
if ("Ruby" in jvmLanguages) {
    println("Ruby is a JVM language")
val favLang = mapOf("Harsh" to "Ruby", "Varshini" to "Kotlin", "Vinayak" to "JavaScript")
if ("Astha" !in favLang) {
    println("Astha has not decided what her favorite language is.")
if ("Java" !in favLang.values) {
    println("No one likes Java :(")

We can do the same thing with ranges as well.

val myAge = 20
if (myAge !in 13..19) {
    println("I am no longer a teenager")


We use when for dealing with more than 2 branches. This has some very powerful syntax that improves from C-like languages with the switch case syntax.

val age: Int = 19 

val undergradAges = arrayOf(18, 19, 20, 21, 22, 23, 24)
when (age) {
    1 -> print("home")
    2 -> print("day care")
    3, 4, 5 -> print("pre-school")
    in 6..17 -> print("school") // ranges
    in undergradAges -> print("undergrad") // collections
    else -> print("Invalid age")

It works with single values, several values collected, ranges and collections as well as many more complex matchers.

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