What is Kotlin - Interactive Quiz & Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print a greeting in Kotlin.

Kotlin

fun main() {
    println([1])
}

Drag options to blanks, or click blank then click option'

A"Hello, Kotlin!"

BHello, Kotlin!

Cprint("Hello, Kotlin!")

Decho "Hello, Kotlin!"

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the quotes around the text.

Using print instead of println without parentheses.

In Kotlin, println prints text to the screen. The text must be inside quotes.

2fill in blank

medium

Complete the code to declare a variable holding the number 10.

Kotlin

fun main() {
    val number: Int = [1]
    println(number)
}

Drag options to blanks, or click blank then click option'

A10

BNumber

Cten

D"10"

Attempts:

3 left

💡 Hint

Common Mistakes

Putting the number inside quotes, making it a string.

Using a word instead of a number.

In Kotlin, numbers are written without quotes. Quotes make them text.

3fill in blank

hard

Fix the error in the function declaration by completing the blank.

Kotlin

fun greet() : [1] {
    return "Hello"
}

Drag options to blanks, or click blank then click option'

AInt

BString

CUnit

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Using Unit or void which mean no return value.

Using Int which is for numbers.

The function returns a text string, so its return type must be String.

4fill in blank

hard

Fill both blanks to create a list of numbers from 1 to 5.

Kotlin

fun main() {
    val numbers = listOf([1], [2], 3, 4, 5)
    println(numbers)
}

Drag options to blanks, or click blank then click option'

A1

B2

C"1"

D"2"

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around numbers, making them strings.

Using wrong numbers or text.

The list holds numbers, so use numbers without quotes.

5fill in blank

hard

Fill all three blanks to create a function that adds two numbers and returns the result.

Kotlin

fun add([1]: Int, [2]: Int) : [3] {
    return a + b
}

Drag options to blanks, or click blank then click option'

Aa

Bb

CInt

DString

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong parameter names that don't match the return statement.

Using String as return type instead of Int.

The function parameters are two integers named a and b, and it returns an integer.

Practice

1. What is Kotlin primarily used for?

easy

A. Creating spreadsheets

B. Designing websites with HTML

C. Managing databases

D. Writing software applications

Solution

1. Step 1: Understand Kotlin's purpose

   Kotlin is a programming language designed to write software applications.

2. Step 2: Compare with other options

   HTML is for websites, databases need SQL, spreadsheets use Excel, so these are not Kotlin's main use.

3. Final Answer:

   Writing software applications -> Option D

4. Quick Check:

   Kotlin = software applications [OK]

Hint: Kotlin is a programming language, not a design or data tool [OK]

Common Mistakes:

• Confusing Kotlin with HTML or SQL
• Thinking Kotlin is for spreadsheets
• Assuming Kotlin is only for Android apps

2. Which of the following is the correct way to declare a variable in Kotlin?

easy

A. let name = "John"

B. var name: String = "John"

C. string name = "John"

D. dim name as String = "John"

Solution

1. Step 1: Recall Kotlin variable syntax

   Kotlin uses var or val to declare variables with type after colon.

2. Step 2: Check each option

   var name: String = "John" uses var name: String = "John", which is correct Kotlin syntax. Others use syntax from other languages.

3. Final Answer:

   var name: String = "John" -> Option B

4. Quick Check:

   Kotlin variable = var name: Type = value [OK]

Hint: Kotlin uses var or val with colon for type [OK]

Common Mistakes:

• Using let instead of var or val
• Writing type before variable name
• Using keywords from other languages

3. What will be the output of this Kotlin code?

fun main() {
    val greeting = "Hello"
    val name = "Anna"
    println("$greeting, $name!")
}

medium

A. Hello, Anna!

B. $greeting, $name!

C. greeting, name!

D. Hello Anna

Solution

1. Step 1: Understand string interpolation in Kotlin

   Kotlin uses $variable inside strings to insert variable values.

2. Step 2: Apply interpolation to variables

   Here, $greeting becomes "Hello" and $name becomes "Anna".

3. Final Answer:

   Hello, Anna! -> Option A

4. Quick Check:

   String interpolation = Hello, Anna! [OK]

Hint: Look for $variable inside strings for interpolation [OK]

Common Mistakes:

• Printing variable names instead of values
• Missing commas or punctuation in output
• Confusing Kotlin with other languages' string syntax

4. Identify the error in this Kotlin code:

fun main() {
    val number = 10
    number = 20
    println(number)
}

medium

A. Missing semicolon after println

B. Wrong function name

C. Cannot reassign a val variable

D. Variable type not declared

Solution

1. Step 1: Understand val vs var in Kotlin

   val declares a read-only variable that cannot be reassigned.

2. Step 2: Check reassignment in code

   The code tries to assign 20 to number after declaring it as val, causing an error.

3. Final Answer:

   Cannot reassign a val variable -> Option C

4. Quick Check:

   val = read-only, no reassignment [OK]

Hint: val means constant, cannot change value later [OK]

Common Mistakes:

• Thinking val allows reassignment
• Assuming semicolons are required
• Confusing val with var

5. You want to write a Kotlin program that works well with existing Java code and helps avoid common errors. Which feature of Kotlin helps with this?

hard

A. Null safety to prevent null pointer errors

B. Using semicolons to end statements

C. Writing all code in one file

D. Avoiding functions and using only variables

Solution

1. Step 1: Identify Kotlin features for safety

   Kotlin has null safety features that help avoid null pointer exceptions common in Java.

2. Step 2: Evaluate other options

   Semicolons are optional, writing all code in one file is not required, and avoiding functions is not practical.

3. Final Answer:

   Null safety to prevent null pointer errors -> Option A

4. Quick Check:

   Kotlin null safety = fewer errors [OK]

Hint: Kotlin's null safety avoids common Java errors [OK]

Common Mistakes:

• Thinking semicolons improve safety
• Believing all code must be in one file
• Ignoring functions in Kotlin