FAQ: Introduction to Kotlin - Errors and Bugs

This community-built FAQ covers the “Errors and Bugs” exercise from the lesson “Introduction to Kotlin”.

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This exercise can be found in the following Codecademy content:

Learn Kotlin

FAQs on the exercise Errors and Bugs

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What does “character number” mean? As in “The second number ( 3 ) tells us the character number in which the error lives on that line.”

It tells you the number of characters, starting from the left, where the error shows up.

fun main() {
  printlnn("An error a day keeps the programmer away.")

In this case, it tells you 3 because starting on line 2, from the very left, you have two spaces and then the letter p, which accounts for the third character, and thus your number (3). As our error is part of the entire println, it tells you where it begins. If you were to remove the closing parenthesis, for example, the error would be at character 54.

I am getting this error on self grading quiz project:

Quiz.kt:31:7: error: operator '==' cannot be applied to 'Int!' and 'String'
  if (studentAnswer3 == quizAnswer3) {
Quiz.kt:33:14: error: operator '==' cannot be applied to 'Int!' and 'String'
  } else if (studentAnswer3 == "equilateral") {

This is my code:

fun main() {
  val quizAnswer1 = 15
  var quizAnswer2 = 3
  val quizAnswer3 = "isosceles"
  val quizAnswer4 = 47

  // Write your code below
  println("What is 75 / 5?")
  val studentAnswer1 = Integer.valueOf(readLine())
  println("What is 6 * 2y?")
  val studentAnswer2 = Integer.valueOf(readLine())
  println("What triangle has two equal sides?")
  val studentAnswer3 = Integer.valueOf(readLine())
  println("What is 8 * 6 - (3 - 2)?")
  val studentAnswer4 = Integer.valueOf(readLine())
  var points = 0

  if (studentAnswer1 == quizAnswer1) {
    points += 25

  if (studentAnswer2 == quizAnswer2) {
    points += 25
  } else if (studentAnswer2 == quizAnswer2++ || studentAnswer2 == quizAnswer2--) {
    points += 20
    println("The answer $studentAnswer2 is within 1 point of $quizAnswer2")
  } else {
    points += 1

  if (studentAnswer3 == quizAnswer3) {
    points += 25
  } else if (studentAnswer3 == "equilateral") {
    points += 10
  } else {
    points += 1

  if (studentAnswer4 == quizAnswer4) {
    points += 25
  } else if (studentAnswer4 in 44..54) {
    points += 20
  } else {
    points += 1

  when (points) {
    in 0..59 -> println("$points points is an F.")
    in 60..69 -> println("$points points is an D.")
    in 70..79 -> println("$points points is an C.")
    in 80..89 -> println("$points points is an B.")
    in 90..100 -> println("$points points is an A.")
    in 101..110 -> println("$points points is an A+.")

With Kotlin, you cannot attempt to compare values of different data types.

studentAnswer3 is being assigned an Integer, whereas quizAnswer3 is a String.

If you know for a fact that studentAnswer3 will always be compared against a String, then that’s the datatype it should receive :slight_smile:

How do I change the datatypes.

What is the purpose of Integer.valueOf(readLine()), and why are we using it here?