Let function with safe calls in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to safely print the length of the string using let.

Kotlin

val name: String? = "Kotlin"
name[1] { println(it.length) }

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

A.let

B?.let

C?:let

D!!let

Attempts:

3 left

💡 Hint

Common Mistakes

Using .let without safe call causes error if variable is null.

Using !!let is invalid syntax.

Using ?:let is incorrect because ?: is the Elvis operator.

The safe call operator ?. is used before let to ensure the block runs only if 'name' is not null.

2fill in blank

medium

Complete the code to safely convert the string to uppercase using let.

Kotlin

val input: String? = "hello"
val result = input[1] { it.uppercase() } ?: "default"

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

A.let

B?:let

C!!let

D?.let

Attempts:

3 left

💡 Hint

Common Mistakes

Using .let without safe call causes NullPointerException if input is null.

Using !!let is invalid syntax.

Using ?:let is incorrect; ?: is the Elvis operator.

Using ?.let ensures the uppercase conversion happens only if 'input' is not null; otherwise, "default" is used.

3fill in blank

hard

Fix the error in the code to safely print the first character of the string using let.

Kotlin

val text: String? = null
text[1] { println(it.first()) }

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

A.let

B!!let

C?.let

D?:let

Attempts:

3 left

💡 Hint

Common Mistakes

Using .let without safe call causes NullPointerException.

Using !!let is invalid syntax.

Using ?:let is incorrect.

The safe call operator ?. before let prevents calling let on a null value, avoiding runtime errors.

4fill in blank

hard

Fill both blanks to safely print the length of the string if it is not null and longer than 3 characters.

Kotlin

val word: String? = "code"
word[1] { if (it.length [2] 3) println(it.length) }

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

A?.let

B>

C<

D.let

Attempts:

3 left

💡 Hint

Common Mistakes

Using .let without safe call causes error if word is null.

Using < instead of > changes the logic.

Using ?:let is invalid.

Use ?.let to safely call let only if word is not null, and > to check if length is greater than 3.

5fill in blank

hard

Fill all three blanks to create a list of lengths only for words longer than 4 characters.

Kotlin

val words: List<String?> = listOf("apple", "bat", "carrot")
val lengths = words.mapNotNull { it[1] { if (it.length [2] 4) it[3] { it.length } else null } }
println(lengths)

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

A?.let

B>

C<

D.let

Attempts:

3 left

💡 Hint

Common Mistakes

Using .let without safe call causes errors if any word is null.

Using < instead of > changes the filter condition.

Misplacing .let inside the lambda.

Use ?.let to safely call let on each word, > to check length, and .let inside the lambda to return length or null.