Challenge 3: Smart Casts — Solution

fun describeAge(age: Int?) {
    if (age != null) {
        // Smart-cast: age is treated as Int (not Int?) inside this block
        if (age % 2 == 0) {
            println("Age $age is even")
        } else {
            println("Age $age is odd")
        }
    } else {
        println("Age unknown")
    }
}

fun main() {
    describeAge(33)
    describeAge(40)
    describeAge(null)
}

/*
Output:
Age 33 is odd
Age 40 is even
Age unknown

Notes:
- Inside the "if (age != null)" branch, Kotlin smart-casts age from Int?
  to Int automatically — age % 2 works directly, with no ?. or !! needed.
- The smart cast only applies because age is a val parameter that can't
  change between the check and the use; Kotlin wouldn't smart-cast a
  mutable var property that another thread could modify in between.
- The else branch handles the null case explicitly, so every possible
  input is covered without ever forcing a value with !!.
*/