Vararg parameters in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a function that accepts a variable number of integers.

Kotlin

fun printNumbers([1] numbers: Int) {
    for (number in numbers) {
        println(number)
    }
}

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

Aval

Bvar

Cvararg

Dconst

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'val' or 'var' instead of 'vararg' for variable arguments.

Forgetting to add the keyword before the parameter name.

The vararg keyword allows the function to accept a variable number of arguments.

2fill in blank

medium

Complete the code to call the function with multiple integer arguments.

Kotlin

printNumbers([1])

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

A1, 2, 3

BlistOf(1, 2, 3)

CarrayOf(1, 2, 3)

DsetOf(1, 2, 3)

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a list or array directly without the spread operator.

Using a collection type instead of separate arguments.

When calling a function with vararg parameters, you can pass multiple arguments separated by commas.

3fill in blank

hard

Fix the error in calling the function with an array argument.

Kotlin

val nums = intArrayOf(4, 5, 6)
printNumbers([1] nums)

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

Anums

B*

C*@

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the array variable directly without the spread operator.

Using incorrect symbols like '*@' or repeating '*'.

Use the spread operator * before the array to pass its elements as separate arguments.

4fill in blank

hard

Fill both blanks to define a function that accepts a string and a variable number of integers.

Kotlin

fun showDetails(name: String, [1] numbers: [2]) {
    println("Name: $name")
    for (num in numbers) {
        println(num)
    }
}

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

Avararg

BIntArray

CInt

DArray<Int>

Attempts:

3 left

💡 Hint

Common Mistakes

Using array types like IntArray or Array instead of the element type.

Omitting the vararg keyword.

The vararg keyword is used before the parameter name, and the type is Int for variable integers.

5fill in blank

hard

Fill all three blanks to create a function that sums variable integers and returns the result.

Kotlin

fun sumNumbers([1] nums: [2]): [3] {
    var total = 0
    for (n in nums) {
        total += n
    }
    return total
}

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

Avararg

BInt

DDouble

Attempts:

3 left

💡 Hint

Common Mistakes

Using Double as return type when summing integers.

Omitting vararg keyword.

The function uses vararg for variable arguments of type Int and returns an Int sum.

Practice

1.

What does the vararg keyword do in Kotlin functions?

easy

A. Allows passing a variable number of arguments to a function

B. Declares a function that returns multiple values

C. Defines a function with no parameters

D. Specifies a function that accepts only one argument

Solution

1. Step 1: Understand the purpose of vararg

   The vararg keyword lets a function accept zero or more arguments of the same type without needing an array or list explicitly.

2. Step 2: Compare options with this meaning

   Only Allows passing a variable number of arguments to a function correctly describes this behavior, while others describe unrelated function features.

3. Final Answer:

   Allows passing a variable number of arguments to a function -> Option A

4. Quick Check:

   Vararg = variable arguments [OK]

Hint: Vararg means many arguments, not just one [OK]

Common Mistakes:

• Thinking vararg returns multiple values
• Confusing vararg with no parameters
• Assuming vararg limits to one argument

2.

Which of the following is the correct syntax to declare a function with a vararg parameter in Kotlin?

fun printAll(____ numbers: Int) { for (n in numbers) println(n) }

easy

A. var

B. varargs

C. vararg

D. args

Solution

1. Step 1: Recall the exact keyword for variable arguments

   Kotlin uses vararg (singular) to declare variable number of arguments.

2. Step 2: Check each option

   Only vararg matches the correct keyword; others are incorrect or invalid syntax.

3. Final Answer:

   vararg -> Option C

4. Quick Check:

   Keyword is vararg, not varargs [OK]

Hint: Remember: vararg is singular keyword [OK]

Common Mistakes:

• Using 'varargs' instead of 'vararg'
• Omitting the keyword entirely
• Using 'var' or 'args' which are invalid here

3.

What is the output of this Kotlin code?

fun sumAll(vararg numbers: Int): Int { var sum = 0; for (n in numbers) sum += n; return sum }

fun main() {
  println(sumAll(1, 2, 3))
  println(sumAll())
}

medium

A. Error and error

B. 6 and error

C. Error and 0

D. 6 and 0

Solution

1. Step 1: Understand the function behavior with vararg

   The function sums all integers passed. If no arguments, the loop does not run, sum stays 0.

2. Step 2: Calculate outputs for calls

   sumAll(1,2,3) = 1+2+3 = 6; sumAll() = 0 (no arguments)

3. Final Answer:

   6 and 0 -> Option D

4. Quick Check:

   Sum of inputs or zero if none [OK]

Hint: Vararg can be empty, sum then zero [OK]

Common Mistakes:

• Assuming empty vararg causes error
• Forgetting sum starts at zero
• Confusing vararg with list requiring explicit array

4.

Identify the error in this Kotlin function declaration:

fun printNames(vararg names: String, age: Int) {
  for (name in names) println(name)
  println(age)
}

medium

A. Function cannot have more than one parameter

B. Vararg parameter must be the last parameter

C. Vararg parameter cannot be of type String

D. Vararg parameters must be declared with 'varargs'

Solution

1. Step 1: Recall vararg parameter position rule

   Kotlin requires the vararg parameter to be the last in the parameter list.

2. Step 2: Check the function parameters

   Here, vararg names is before age, which is invalid syntax.

3. Final Answer:

   Vararg parameter must be the last parameter -> Option B

4. Quick Check:

   Vararg last parameter rule [OK]

Hint: Vararg must always be last parameter [OK]

Common Mistakes:

• Placing vararg parameter before others
• Thinking vararg can be anywhere
• Using 'varargs' instead of 'vararg'

5.

Given this function:

fun combine(vararg parts: String): String {
  return parts.joinToString(separator = ", ")
}

Which call correctly passes an existing array val arr = arrayOf("a", "b", "c") to combine?

hard

A. combine(*arr)

B. combine(arr)

C. combine(arr.toList())

D. combine(arr as String)

Solution

1. Step 1: Understand how to pass an array to vararg

   Kotlin requires the spread operator * to pass an array as vararg arguments.

2. Step 2: Evaluate each option

   combine(*arr) uses *arr, correctly spreading the array. combine(arr) passes the array as a single argument, not vararg. combine(arr.toList()) passes a list, not vararg. combine(arr as String) is invalid cast.

3. Final Answer:

   combine(*arr) -> Option A

4. Quick Check:

   Use * to spread array for vararg [OK]

Hint: Use * to spread array into vararg [OK]

Common Mistakes:

• Passing array without * operator
• Passing list instead of array
• Trying invalid casts to String