Parameters with default values in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of function with default parameters

What is the output of this Kotlin code?

Kotlin

fun greet(name: String = "Guest", greeting: String = "Hello") {
    println("$greeting, $name!")
}

greet()
greet("Alice")
greet(greeting = "Hi")

A

Hello, Guest!
Hello, Alice!
Hello, Guest!

B

Hi, Guest!
Hello, Alice!
Hi, Guest!

C

Hello, Guest!
Hi, Alice!
Hi, Guest!

D

Hello, Guest!
Hello, Alice!
Hi, Guest!

💡 Hint

Remember that default parameters are used when no argument is provided for that parameter.

The function greet uses default values for both parameters. When called without arguments, it prints "Hello, Guest!". When called with "Alice", it uses the default greeting "Hello". When called with named argument greeting = "Hi", it uses default name "Guest".

❓ Predict Output

intermediate

Function call with mixed default and explicit parameters

What will this Kotlin code print?

Kotlin

fun calculate(price: Int, tax: Double = 0.1, discount: Double = 0.0): Double {
    return price * (1 + tax) * (1 - discount)
}

println(calculate(100))
println(calculate(100, discount = 0.2))
println(calculate(100, 0.2))

A

110.0
88.0
120.0

B

110.0
80.0
100.0

C

110.0
80.0
120.0

D

110.0
88.0
100.0

💡 Hint

Check which parameters are passed explicitly and which use default values.

First call uses default tax 0.1 and discount 0.0: 100 * 1.1 * 1 = 110.0. Second call overrides discount to 0.2 but uses default tax 0.1: 100 * 1.1 * 0.8 = 88.0 (but option A says 80.0, so check carefully). Third call passes tax=0.2 and discount default 0.0: 100 * 1.2 * 1 = 120.0. So option A's second output is wrong, correct is 88.0. So option A is correct.

🔧 Debug

advanced

Identify the error in default parameter usage

This Kotlin function has a problem. What error will it cause?

Kotlin

fun printMessage(message: String = "Hello", times: Int) {
    repeat(times) {
        println(message)
    }
}

printMessage(times = 3)

A Prints "Hello" three times

B Runtime error: times is null

C Compilation error: Non-default parameter 'times' cannot follow default parameter 'message'

D Compilation error: Missing argument for parameter 'times'

💡 Hint

In Kotlin, parameters with default values must be declared after parameters without default values.

Kotlin requires that parameters with default values come after parameters without default values. Here, 'message' has a default but comes before 'times' which has no default. This causes a compilation error.

❓ Predict Output

advanced

Output with multiple default parameters and named arguments

What is the output of this Kotlin code?

Kotlin

fun describe(color: String = "red", shape: String = "circle", size: Int = 5) {
    println("$size $color $shape")
}

describe()
describe(shape = "square")
describe(size = 10, color = "blue")

A

5 red circle
5 square red
10 blue circle

B

5 red circle
5 red square
10 blue circle

C

5 red circle
square 5 red
10 blue circle

D

5 red circle
5 red square
5 blue circle

💡 Hint

Named arguments let you skip parameters and specify only some values.

First call uses all defaults: 5 red circle. Second call overrides shape to square, others default: 5 red square. Third call overrides size and color, shape default: 10 blue circle.

🧠 Conceptual

expert

Behavior of default parameters with inheritance

Consider these Kotlin classes: class Base { open fun greet(name: String = "Guest") { println("Hello, $name") } } class Derived : Base() { override fun greet(name: String) { println("Hi, $name") } } val obj: Base = Derived() obj.greet()

A Hi, Guest

B Runtime error: No default argument found

C Compilation error: Default parameter missing in override

D Hello, Guest

💡 Hint

Default parameter values are resolved at compile time based on the reference type.

In Kotlin, default parameter values are determined by the compile-time type. Here, obj is of type Base, so greet() uses Base's default parameter "Guest". The overridden greet in Derived does not have a default, but it is called with the default argument from Base, so it prints "Hi, Guest".