Iterating collections with forEach in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the forEach function do in Kotlin collections?

It runs a given block of code on each item in the collection, one by one.

beginner

How do you write a forEach loop to print each element in a list called numbers?

numbers.forEach { number -> println(number) }

intermediate

Can you modify elements inside a forEach loop in Kotlin?

No, forEach is used for actions like printing or logging. To change elements, use map or other transformation functions.

intermediate

What is the difference between a for loop and forEach in Kotlin?

for is a language construct that can be used with any iterable, while forEach is a function that takes a lambda and runs it on each element.

beginner

Write a forEach example that prints each string in a list with its length.

val words = listOf("apple", "banana", "cherry") words.forEach { word -> println("$word has ${word.length} letters") }

What type of argument does forEach take in Kotlin?

A A string value

B An integer index

C A lambda function that takes each element

D A Boolean condition

forEach takes a lambda function that is called for each element in the collection.

Which of these is a correct way to use forEach on a list items?

A forEach(items) { println(it) }

B items.forEach -> println(it)

C items.forEach(println(it))

D items.forEach { println(it) }

The correct syntax is calling forEach on the collection with a lambda: items.forEach { println(it) }.

Can forEach be used to change the elements of a mutable list directly?

A No, it is for performing actions only

B Yes, it modifies elements automatically

C Only if the list is immutable

D Only with a special keyword

forEach is for running code on each element, not for changing elements. Use map or direct indexing for changes.

What will this code print?

listOf(1, 2, 3).forEach { println(it * 2) }

A 2 4 6

B 1 2 3

C Error

D 6 4 2

Each element is multiplied by 2 and printed: 2, 4, 6.

Which Kotlin collection function is best for transforming elements instead of just iterating?

A forEach

B map

C filter

D reduce

map creates a new collection by transforming each element.

Explain how to use forEach to print all elements in a Kotlin list.

Think about how you tell the list to do something with each item.

Describe the difference between forEach and a for loop in Kotlin.

Consider how each handles looping and control flow.