While loop in Kotlin Programming Language

Question

In my kotlin code i am getting Type mismatch(inferred type is Int but Boolean was expected) error.

fun main(args: Array<String>) {
   var i = args.size 
   while (i--){
    println(args[i])
   }
}

What is unclear? while expects a boolean expression. i-- is of type Int. — JB Nizet, Jun 01 '17 at 06:52

score 3 · Accepted Answer · answered Jun 01 '17 at 06:51

3

You have to provide a Boolean value as the argument of while. There's no auto-casting of Int to Boolean in Kotlin.

So you can't do while(i--), but you can, for example, do while(i-- != 0) or while(i-- > 0).

answered Jun 01 '17 at 06:51

zsmb13

score 2 · Answer 2 · answered Jun 01 '17 at 06:56

2

while (x > 0) {
    x--
}

do {
    val y = retrieveData()
} while (y != null) // y is visible here!

answered Jun 01 '17 at 06:56

LF00

score 1 · Answer 3 · answered Jun 01 '17 at 06:52

1

while expects a boolean (true/false), you give an integer (i-1). correct code could be:

fun main(args: Array<String>) {
   var i = args.size 
   while (i>=0){
    println(args[i])
    i--
   }
}

answered Jun 01 '17 at 06:52

Fabian

3 Answers3