For loop over collections in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a for loop over a list

What is the output of this Kotlin code?

Kotlin

val fruits = listOf("apple", "banana", "cherry")
for (fruit in fruits) {
    print(fruit.first())
}

A a b c

B applebananacherry

C abc

D fruitfruitfruit

💡 Hint

Look at what the print statement outputs for each fruit.

The loop prints the first character of each fruit name without spaces, so the output is 'abc'.

❓ Predict Output

intermediate

For loop with index over a list

What will be printed by this Kotlin code?

Kotlin

val numbers = listOf(10, 20, 30)
for ((index, value) in numbers.withIndex()) {
    println("$index:$value")
}

A

0:10
1:20
2:30

B

index:value
index:value
index:value

C

10:0
20:1
30:2

D

0-10
1-20
2-30

💡 Hint

withIndex() gives pairs of index and value.

The loop prints each index and its corresponding value separated by a colon, each on a new line.

🔧 Debug

advanced

Identify the error in this for loop over a map

What error does this Kotlin code produce?

Kotlin

val map = mapOf("a" to 1, "b" to 2)
for (key, value in map) {
    println("$key -> $value")
}

A SyntaxError: Unexpected destructuring declaration

B TypeError: Cannot iterate over map

C No error, prints 'a -> 1' and 'b -> 2'

D RuntimeException: Invalid loop variable

💡 Hint

Check how to destructure map entries in Kotlin for loops.

The for loop syntax for destructuring map entries requires parentheses around the pair: for ((key, value) in map). Missing parentheses cause a syntax error.

❓ Predict Output

advanced

Output of nested for loops over collections

What is the output of this Kotlin code?

Kotlin

val list1 = listOf(1, 2)
val list2 = listOf("a", "b")
for (num in list1) {
    for (char in list2) {
        print("$num$char ")
    }
}

A 1 2 a b

B 1a 1b 2a 2b

C a1 b1 a2 b2

D 12 ab

💡 Hint

The outer loop runs over numbers, inner over characters.

The code prints each number combined with each character, separated by spaces, in order.

🧠 Conceptual

expert

Number of iterations in a for loop over a set

Given this Kotlin code, how many times will the loop run?

Kotlin

val set = setOf("x", "y", "z")
var count = 0
for (item in set) {
    count++
}
println(count)

A Cannot determine because sets are unordered

B 0

C 1

D 3

💡 Hint

Count how many items are in the set.

The set has 3 unique items, so the loop runs 3 times, incrementing count each time.