Similarly to the if statement, when can also be used as an expression. To do this, create a variable and assign when as an expression as follows:

fun main(args: Array<String>) {
    val grade = "A"
    val remarks = when (grade) {
        "A","a" -> "Excellent"
         "B","b" -> "Very Good"
         "C","c" -> "Nice work"
         "D","d" -> "OK"
         "E","e" -> "Hmmm"
         "F","f" -> "Better luck next time"
         else -> "Invalid input"
     }
      println(remarks)
  }