I Want to return to question if user write other words than "Yes" "No" in my code with if/else

Question

I Want to return to question if user write other words than "Yes" "No" in my code with if/else.

You only answer with "YES" or "NO" but answer like"sjfkhs" make me sad. if somebody write like "sdjk" i want to repeat the question.

fun main(args: Array<String>) {

    var CanI_Play: String
    var IfUrMotherDisturb: String
    var HaveYouFreeTime: String
var Question1 = "Can I play?"
    println(Question1)
    CanI_Play = readLine()!!.toUpperCase() //wstawienie !!. mówi komputerowi , że nie wprowadzimy null
    // czyli chyba pustego pola które w tym przypadku bedzie zmienione z małych liter na duże

    if (CanI_Play=="YES") {
    println("So you can play from now")
    }
    if (CanI_Play=="NO") {
        println("You can't play yet...:(")
        println("Have You free time?")
        HaveYouFreeTime = readLine()!!.toUpperCase()
        if (HaveYouFreeTime=="NO") {
            println("Do what You should do and You can play")
        }
        if (HaveYouFreeTime=="YES") {
            println("If Your mother disturb?")
            IfUrMotherDisturb = readLine()!!.toUpperCase()

            if (IfUrMotherDisturb=="YES"){
                println("Bad news. Time to look for new house. OMFG")
            }
            if (IfUrMotherDisturb=="NO"){
                println("Great news! You can play!")
            }
            else{
                println("I Want to return to question IfUrMotherDisturb")
            }







        }
        else{
            println("I want to return to question HaveYouFreeTime")
        }

    }
    else{
        println("I want to return to question CanI_Play")
    }


}

Answer 1

This is not possible in the general case using only if/else. One option would be to use a loop, while another would be to use recursion. I will demonstrate how to do both. I have slightly changed your code to match standard Kotlin naming conventions and style. If you are taking some kind of class, and you are required to follow a specific convention for that class, disregard my changes. Here is the changed question code:

fun main() {
    println("Can I play?")
    val canIPlay = readLine()!!.toUpperCase()
    if (canIPlay == "YES") {
        println("So you can play from now")
    }
    if (canIPlay == "NO") {
        println("You can't play yet...:(")
        println("Have You free time?")
        val haveYouFreeTime = readLine()!!.toUpperCase()
        if (haveYouFreeTime == "NO") {
            println("Do what You should do and You can play")
        }
        if (haveYouFreeTime == "YES") {
            println("If Your mother disturb?")
            val ifUrMotherDisturb = readLine()!!.toUpperCase()

            if (ifUrMotherDisturb == "YES") {
                println("Bad news. Time to look for new house. OMFG")
            }
            if (ifUrMotherDisturb == "NO") {
                println("Great news! You can play!")
            } else {
                println("I Want to return to question IfUrMotherDisturb")
            }
        } else {
            println("I want to return to question HaveYouFreeTime")
        }
    } else {
        println("I want to return to question CanI_Play")
    }
}

Here is how to solve this problem with recursion:

fun main() {
    askIfCanPlay()
}

fun askIfCanPlay() {
    println("Can I play?")
    val canIPlay = readLine()!!.toUpperCase()
    if (canIPlay == "YES") {
        println("So you can play from now")
    }
    if (canIPlay == "NO") {
        askIfFreeTime()
    } else {
        askIfCanPlay()
    }
}

fun askIfFreeTime() {
    println("You can't play yet...:(")
    println("Have You free time?")
    val haveYouFreeTime = readLine()!!.toUpperCase()
    if (haveYouFreeTime == "NO") {
        println("Do what You should do and You can play")
    }
    if (haveYouFreeTime == "YES") {
        askIfMotherDisturb()
    } else {
        askIfFreeTime()
    }
}

fun askIfMotherDisturb() {
    println("If Your mother disturb?")
    val ifUrMotherDisturb = readLine()!!.toUpperCase()

    if (ifUrMotherDisturb == "YES") {
        println("Bad news. Time to look for new house. OMFG")
    }
    if (ifUrMotherDisturb == "NO") {
        println("Great news! You can play!")
    } else {
        askIfMotherDisturb()
    }
}

Here is how to solve this problem with while loops:

fun main() {
    var canIPlay = ""
    while(!(canIPlay == "YES" || canIPlay == "NO")){
        println("Can I play?")
        canIPlay = readLine()!!.toUpperCase()
    }

    if (canIPlay == "YES") {
        println("So you can play from now")
    }
    else if (canIPlay == "NO") {
        println("You can't play yet...:(")
        var haveYouFreeTime = ""
        while(!(haveYouFreeTime == "YES" || haveYouFreeTime == "NO")){
            println("Have You free time?")
            haveYouFreeTime = readLine()!!.toUpperCase()
        }
        if (haveYouFreeTime == "NO") {
            println("Do what You should do and You can play")
        }
        if (haveYouFreeTime == "YES") {
            var ifUrMotherDisturb = ""
            while(!(ifUrMotherDisturb == "YES" || haveYouFreeTime == "NO")){
                println("If Your mother disturb?")
                ifUrMotherDisturb = readLine()!!.toUpperCase()
            }

            if (ifUrMotherDisturb == "YES") {
                println("Bad news. Time to look for new house. OMFG")
            }
            if (ifUrMotherDisturb == "NO") {
                println("Great news! You can play!")
            } else {
                assert(false)// this will never happen
            }
        } else {
            assert(false)// this will never happen
        }
    }else {
        assert(false)//this will never happen
    }
}

I personally prefer the recursive method, especially since kotlin aims to be a more functional language.