Array creation and usage in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an array of integers with values 1, 2, and 3.

Kotlin

val numbers = arrayOf([1])

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

A1 2 3

B1, 2, 3

C[1, 2, 3]

D(1, 2, 3)

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting commas between values.

Using square brackets instead of parentheses.

The arrayOf function takes comma-separated values to create an array. So arrayOf(1, 2, 3) creates an array with elements 1, 2, and 3.

2fill in blank

medium

Complete the code to access the second element of the array named fruits.

Kotlin

val secondFruit = fruits[[1]]

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

A0

B-1

C2

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 2 instead of 1 for the second element index.

Using negative indices which are not valid in Kotlin arrays.

Arrays in Kotlin are zero-indexed, so the first element is at index 0 and the second element is at index 1.

3fill in blank

hard

Fix the error in the code to create an array of size 5 filled with zeros.

Kotlin

val zeros = Array([1] = 5) { 0 }

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

Acount

Blength

Csize

Dcapacity

Attempts:

3 left

💡 Hint

Common Mistakes

Using length or count which are not parameter names here.

Using capacity which is not valid for Kotlin arrays.

The Array constructor in Kotlin takes the size as the first argument. The correct parameter name is size.

4fill in blank

hard

Fill both blanks to create an array of strings with values "apple", "banana", and "cherry".

Kotlin

val fruits = arrayOf([1]) // Create array
val firstFruit = fruits[[2]] // Access first element

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

A"apple", "banana", "cherry"

B0

C1

D"apple"

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 1 to access the first element.

Not using quotes around string values.

The arrayOf function takes comma-separated string values to create the array. The first element is at index 0.

5fill in blank

hard

Fill all three blanks to create an array of integers from 1 to 5, square each number, and filter out squares greater than 10.

Kotlin

val numbers = arrayOf(1, 2, 3, 4, 5)
val squares = numbers.map { it [1] [2] }
val filtered = squares.filter { it [3] 10 }

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

A*

Bit

C<=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition instead of multiplication for squaring.

Using wrong comparison operators in filter.

To square a number, multiply it by itself: it * it. To keep squares less than or equal to 10, use it <= 10.

Practice

1. What is the correct way to create an array of integers with values 1, 2, and 3 in Kotlin?

easy

A. val arr = Array(3) { 1, 2, 3 }

B. val arr = arrayOf(1, 2, 3)

C. val arr = IntArray(1, 2, 3)

D. val arr = [1, 2, 3]

Solution

1. Step 1: Understand array creation syntax

   Kotlin uses arrayOf() to create an array with given elements.

2. Step 2: Check each option

   val arr = arrayOf(1, 2, 3) uses arrayOf(1, 2, 3) which is correct. val arr = [1, 2, 3] uses square brackets which is invalid in Kotlin. val arr = IntArray(1, 2, 3) which uses invalid constructor arguments for IntArray. val arr = Array(3) { 1, 2, 3 } tries to pass multiple values in a lambda which is incorrect.

3. Final Answer:

   val arr = arrayOf(1, 2, 3) -> Option B

4. Quick Check:

   Use arrayOf() for arrays with elements [OK]

Hint: Use arrayOf() to create arrays with elements [OK]

Common Mistakes:

• Using square brackets [] like in other languages
• Confusing IntArray with Array<Int>
• Trying to pass multiple values in Array constructor lambda

2. Which of the following is the correct syntax to create an array of size 5 with all elements initialized to zero in Kotlin?

easy

A. val arr = Array(5, 0)

B. val arr = Array(0, 0, 0, 0, 0)

C. val arr = Array(5) { 0 }

D. val arr = IntArray(5, 0)

Solution

1. Step 1: Understand Array constructor usage

   Kotlin's Array(size) { init } creates an array of given size, initializing each element with the lambda result.

2. Step 2: Evaluate options

   val arr = Array(5) { 0 } correctly uses Array(5) { 0 } to create an array of 5 zeros. val arr = Array(0, 0, 0, 0, 0) is invalid syntax. val arr = Array(5, 0) is invalid syntax. val arr = IntArray(5, 0) is invalid because IntArray constructor takes only size or size with init lambda, not two parameters.

3. Final Answer:

   val arr = Array(5) { 0 } -> Option C

4. Quick Check:

   Use Array(size) { value } to initialize [OK]

Hint: Use Array(size) with lambda to initialize all elements [OK]

Common Mistakes:

• Passing two parameters to Array constructor incorrectly
• Confusing IntArray constructor parameters
• Passing multiple values directly to Array constructor

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

val arr = arrayOf(10, 20, 30)
println(arr[1])

medium

A. 20

B. 10

C. 30

D. IndexOutOfBoundsException

Solution

1. Step 1: Understand array indexing

   Arrays in Kotlin are zero-indexed, so arr[0] is 10, arr[1] is 20, and arr[2] is 30.

2. Step 2: Check the printed value

   The code prints arr[1], which is 20.

3. Final Answer:

   20 -> Option A

4. Quick Check:

   Array index 1 holds 20 [OK]

Hint: Remember arrays start at index 0 in Kotlin [OK]

Common Mistakes:

• Confusing index 1 with first element
• Expecting 30 instead of 20
• Thinking arrays start at 1

4. Identify the error in the following Kotlin code snippet:

val arr = arrayOf(1, 2, 3)
arr[3] = 4
println(arr.joinToString())

medium

A. arr is immutable, cannot assign new value

B. No error, output is '1, 2, 3, 4'

C. Syntax error in array declaration

D. IndexOutOfBoundsException at arr[3] assignment

Solution

1. Step 1: Check array size and indexing

   The array has 3 elements with indices 0, 1, 2. Accessing index 3 is out of bounds.

2. Step 2: Understand runtime behavior

   Assigning arr[3] = 4 causes an IndexOutOfBoundsException at runtime.

3. Final Answer:

   IndexOutOfBoundsException at arr[3] assignment -> Option D

4. Quick Check:

   Array indices must be within 0 to size-1 [OK]

Hint: Array indices go from 0 to size-1 only [OK]

Common Mistakes:

• Trying to assign value outside array bounds
• Thinking array size auto-expands
• Confusing immutability with index errors

5. You want to create an array of size 4 where each element is its index squared (0, 1, 4, 9). Which Kotlin code correctly does this?

hard

A. val arr = Array(4) { index -> index * index }

B. val arr = arrayOf(4) { index -> index * index }

C. val arr = intArrayOf(4) { index -> index * index }

D. val arr = Array(4) { -> it * it }

Solution

1. Step 1: Understand array initialization with lambda

   Kotlin's Array(size) { index -> value } creates an array where each element is initialized by the lambda using the index.

2. Step 2: Check each option

   val arr = Array(4) { index -> index * index } uses explicit lambda parameter index and correctly computes index squared. val arr = arrayOf(4) { index -> index * index } is invalid because arrayOf does not take a size and lambda. val arr = intArrayOf(4) { index -> index * index } is invalid syntax for the intArrayOf factory function. val arr = Array(4) { -> it * it } has invalid lambda syntax where it is undefined.

3. Final Answer:

   val arr = Array(4) { index -> index * index } -> Option A

4. Quick Check:

   Use Array(size) with index lambda for computed values [OK]

Hint: Use Array(size) with index lambda for computed elements [OK]

Common Mistakes:

• Confusing it with index in lambda
• Using arrayOf() for dynamic initialization
• Not using lambda for element computation