Parameters with default values in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a function with a default parameter value.

Kotlin

fun greet(name: String = [1]) {
    println("Hello, $name!")
}

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

A"Guest"

BGuest

C"name"

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to put quotes around string default values.

Using a variable name instead of a value.

In Kotlin, default parameter values must be provided as expressions. Here, "Guest" is a string literal used as the default value.

2fill in blank

medium

Complete the function call to use the default parameter value.

Kotlin

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

greet([1])

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

A(no argument)

B""

C"John"

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Passing an empty string "" instead of no argument.

Passing null which is not allowed without nullable type.

To use the default parameter value, you can call the function without passing any argument, so the blank should be empty.

3fill in blank

hard

Fix the error in the function definition by adding a default value to the parameter.

Kotlin

fun multiply(a: Int, b: Int = [1]): Int {
    return a * b
}

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

A0

B1

C"1"

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string "1" instead of integer 1.

Using null for a non-nullable parameter.

The default value for an Int parameter must be an integer literal. 1 is the multiplicative identity, so it makes sense as a default.

4fill in blank

hard

Fill both blanks to create a function with two parameters, each having default values.

Kotlin

fun formatText(text: String = [1], prefix: String = [2]) {
    println("$prefix$text")
}

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

A"Hello"

B"World"

C"* "

D"- "

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up which default value goes to which parameter.

Forgetting quotes around string defaults.

The first parameter text defaults to "Hello" and the prefix defaults to "* ". Both are string literals.

5fill in blank

hard

Fill all three blanks to define a function with default values and call it with one argument.

Kotlin

fun calculateArea(length: Int = [1], width: Int = [2], unit: String = [3]): String {
    val area = length * width
    return "$area $unit"
}

println(calculateArea(5))

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

A10

B1

C"cm²"

D"m²"

Attempts:

3 left

💡 Hint

Common Mistakes

Using string values for integer parameters.

Omitting quotes around the unit string.

The length defaults to 10, width to 1, and unit to "cm²". Calling calculateArea(5) uses length=5, width=1, unit="cm²".

Practice

1. What happens when you call a Kotlin function with a parameter that has a default value but you don't provide an argument for it?
fun greet(name: String = "Guest") { println("Hello, $name!") }

easy

A. The function uses the default value for the missing parameter.

B. The function throws an error because the argument is missing.

C. The function ignores the parameter and prints nothing.

D. The function requires you to always provide the argument.

Solution

1. Step 1: Understand default parameter behavior

   In Kotlin, if a parameter has a default value, the function can be called without providing that argument.

2. Step 2: Apply to the example function

   Calling greet() will use the default value "Guest" for name, printing "Hello, Guest!".

3. Final Answer:

   The function uses the default value for the missing parameter. -> Option A

4. Quick Check:

   Default parameter means optional argument [OK]

Hint: If argument missing, default value is used automatically [OK]

Common Mistakes:

• Thinking missing argument causes error
• Assuming function ignores missing parameters
• Believing all parameters must be provided

2. Which of the following is the correct way to declare a Kotlin function with a default parameter value?

easy

A. fun add(a: Int, b: Int default 5) { return a + b }

B. fun add(a: Int = 5, b: Int) { return a + b }

C. fun add(a: Int, b: Int) = a + b = 5

D. fun add(a: Int, b: Int = 5) { return a + b }

Solution

1. Step 1: Check Kotlin syntax for default parameters

   In Kotlin, default values are assigned using = after the parameter type, like b: Int = 5.

2. Step 2: Validate each option

   fun add(a: Int, b: Int = 5) { return a + b } correctly uses b: Int = 5. fun add(a: Int = 5, b: Int) { return a + b } places default before non-default parameter, which is allowed but can cause ambiguity if called without named arguments. Options A and C have invalid syntax.

3. Final Answer:

   fun add(a: Int, b: Int = 5) { return a + b } -> Option D

4. Quick Check:

   Default value syntax = parameter: Type = value [OK]

Hint: Use '=' after type to set default value [OK]

Common Mistakes:

• Placing default value before type
• Using 'default' keyword instead of '='
• Assigning default outside parameter list

3. What is the output of the following Kotlin code?

fun multiply(x: Int, y: Int = 2) = x * y

println(multiply(4))

medium

A. 8

B. 4

C. Error: Missing argument for y

D. 2

Solution

1. Step 1: Identify default parameter usage

   The function multiply has a default value of 2 for y. Calling multiply(4) means x=4 and y=2.

2. Step 2: Calculate the result

   Multiply 4 by 2 to get 8.

3. Final Answer:

   8 -> Option A

4. Quick Check:

   Default y=2 used, 4*2=8 [OK]

Hint: If argument missing, default value is used [OK]

Common Mistakes:

• Expecting error for missing argument
• Using only first argument as output
• Confusing default value with zero

4. Identify the error in this Kotlin function declaration:

fun greet(name: String = "User", age: Int) {
    println("Hello, $name! You are $age years old.")
}

medium

A. Cannot use default values with String parameters.

B. Default parameter must be last or followed by named arguments.

C. Function must return a value if default parameters are used.

D. No error, function is correct.

Solution

1. Step 1: Check parameter order rules

   In Kotlin, parameters with default values should be placed after parameters without default values, or you must use named arguments when calling.

2. Step 2: Analyze given function

   Here, name has a default but comes before age which has no default. This causes a problem when calling without named arguments.

3. Final Answer:

   Default parameter must be last or followed by named arguments. -> Option B

4. Quick Check:

   Default parameters after non-default or use named args [OK]

Hint: Place default parameters after non-default ones [OK]

Common Mistakes:

• Putting default parameters before required ones
• Assuming all parameters can have defaults anywhere
• Ignoring named argument calls

5. You want to write a Kotlin function formatMessage that takes a message and an optional prefix with default value "Info:". It should return the combined string. Which function correctly implements this and allows calling with or without the prefix?

hard

A. fun formatMessage(prefix: String = "Info:", message: String) = "$prefix $message"

B. fun formatMessage(message: String, prefix: String) = "$prefix $message"

C. fun formatMessage(message: String, prefix: String = "Info:") = "$prefix $message"

D. fun formatMessage(message: String = "Info:", prefix: String) = "$prefix $message"

Solution

1. Step 1: Define function with default parameter last

   The optional parameter prefix with default value should come after the required message parameter.

2. Step 2: Check each option

   fun formatMessage(message: String, prefix: String = "Info:") = "$prefix $message" correctly places prefix last with default. fun formatMessage(prefix: String = "Info:", message: String) = "$prefix $message" places default before required, which can cause call issues. Options C and D lack default for prefix or have wrong order.

3. Final Answer:

   fun formatMessage(message: String, prefix: String = "Info:") = "$prefix $message" -> Option C

4. Quick Check:

   Default last parameter enables optional argument [OK]

Hint: Put default parameters after required ones for easy calls [OK]

Common Mistakes:

• Placing default parameter before required parameter
• Not providing default value for optional parameter
• Confusing parameter order causing call errors