How to use a while loop to keep looping until condition met with user input kotlin

Question

Using a while loop to keep looping until condition is met.

When pin correct: Displays no message, exits program.

When user inputs wrong pin: Displays correct error message Pin is incorrect, Keeps promting user for input and keeps displaying Pin is incorrect.

When user inputs a non integer data type: Displays correct error message Pin is incorrect, Keeps promting user for input and keeps displaying Pin is incorrect.

Here is my code

fun main() {
    println("Create PIN: ")
    val pin = readln().toIntOrNull()

    println("Enter PIN: ")
    val input = readln().toIntOrNull()

    while (input != pin) {
        if (input == pin) {
            println("PIN is correct")
        }
        else{
            println("Pin is incorrect")
            readln().toIntOrNull()
        }
    }
}

EDIT: I needed to walk away, was feeling like smashing my head against my keyboard haha. Ended up getting it working.

Here's the fix

fun main() {
println("Create PIN: ")
val pin = readln().toIntOrNull()

println("Enter PIN: ")
var input = readln().toIntOrNull()

while (input != pin)
{
    println("PIN is incorrect")
    input = readln().toIntOrNull()
}
if (input == pin){
    println("PIN is correct")
}

}

Tenfour04 · Accepted Answer · 2022-10-05 13:34:37Z

1

I know you already solved it, but just want to share an alternate design pattern you could use in this situation. A while(true) loop keeps running until you call break inside it. It can lead to less code repetition in cases like what you're doing here.

Notice you only have to use readln().toIntOrNull() once instead of twice, and the input variable becomes unnecessary:

fun main() {
    println("Create PIN: ")
    val pin = readln().toIntOrNull()

    println("Enter PIN: ")
    while (true) {
        if (readln().toIntOrNull() == pin) {
            println("PIN is correct")
            break
        }
        println("PIN is incorrect")
    }
}

answered Oct 5, 2022 at 13:34

Tenfour04

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1 Comment

Gilli Over a year ago

I like it thank you

Vojin Purić · Accepted Answer · 2022-10-05 12:32:35Z

0

You forgot to capture newly typed pin. And since you are changing value of the variable you need to use var instead of val

var input = readln().toIntOrNull()

instead of

    else{
        println("Pin is incorrect")
        readln().toIntOrNull()
    }

use

else{
        println("Pin is incorrect")
        input = readln().toIntOrNull()
    }

edited Oct 5, 2022 at 12:32

answered Oct 5, 2022 at 12:02

Vojin Purić

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3 Comments

Gilli Over a year ago

Vojin not sure what you mean by capture newly typed pin? Thanks for the input.

Vojin Purić Over a year ago

Like i wrote in the answer. Same thing you did. you were not saving newly entered input from user

Gilli Over a year ago

Oh I get ya now, was readlining to nothing, but with the edit, readlines to the input?

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