Booleans and Comparisons

A Boolean is a yes/no value: true or false. Comparisons produce Booleans:

fun main() {
    val age = 20

    println(age > 18)
    println(age == 21)
    println(age != 21)
    println("kotlin" == "kotlin")
    println("apple" < "banana")
    println("Ada".equals("ada", ignoreCase = true))
}

true
false
true
true
true
true

Strings compare alphabetically with < and >.

Only Boolean is a condition

A condition must be an actual Boolean. Numbers and strings are never treated as true or false:

fun main() {
    val count = 3
    if (count) {
        println("has items")
    }
}

error: condition type mismatch: inferred type is 'Int' but 'Boolean' was expected.

Write what you mean: if (count > 0), if (name.isNotEmpty()).

Name Boolean variables so they read as yes/no questions: isEnabled, hasAccount, canEdit.