Default parameter values in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

Swift

func greet(name: String = [1]) {
    print("Hello, \(name)!")
}
greet()

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

A"User"

B"Guest"

C"Friend"

D"Visitor"

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to put the default value in quotes.

Using a colon instead of an equals sign for the default value.

The default value for the parameter name is set to "Guest". Calling greet() without arguments prints "Hello, Guest!".

2fill in blank

medium

Complete the code to call the function with a custom argument.

Swift

func greet(name: String = "Guest") {
    print("Hello, \(name)!")
}
greet([1])

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

A"Visitor"

BVisitor

Cname

D"name"

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the argument without quotes.

Passing the parameter name instead of a value.

The function is called with the argument "Visitor" (a string in quotes). This prints "Hello, Visitor!".

3fill in blank

hard

Fix the error in the function definition by completing the default parameter value.

Swift

func multiply(number: Int = [1]) -> Int {
    return number * 2
}
print(multiply())

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

Anil

B"2"

Cnumber

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string "2" instead of integer 2.

Using nil as a default value for a non-optional parameter.

The default value must be an integer (2), not a string or nil. This allows calling multiply() without arguments.

4fill in blank

hard

Fill both blanks to define a function with two parameters, one with a default value.

Swift

func describe(age: Int, city: String = [1]) {
    print("Age: \(age), City: \(city)")
}
describe(age: [2])

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

A"Unknown"

B30

C"Unknown City"

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Using a number as a default for a String parameter.

Not providing the required age argument in the function call.

The parameter city has a default value "Unknown". The function is called with age: 30. The output is "Age: 30, City: Unknown".

5fill in blank

hard

Fill all three blanks to create a function with default parameters and call it with custom arguments.

Swift

func order(item: String = [1], quantity: Int = [2], price: Double = [3]) {
    print("Order: \(quantity) \(item)(s) at $\(price) each")
}
order(item: "Book", quantity: 3, price: 12.99)

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

A"Pen"

B1

C9.99

D"Notebook"

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong types for default values.

Not matching the parameter order in the function call.

The function order has default values: item = "Notebook", quantity = 1, price = 9.99. The call overrides all defaults with custom values.

Practice

1. What is the main purpose of using default parameter values in Swift functions?

easy

A. To make functions run faster

B. To provide fallback values when arguments are not passed

C. To force the caller to always provide arguments

D. To declare variables inside the function

Solution

1. Step 1: Understand default parameters

   Default parameter values allow a function to use a preset value if no argument is provided.

2. Step 2: Identify the purpose

   This makes calling the function easier and avoids errors from missing arguments.

3. Final Answer:

   To provide fallback values when arguments are not passed -> Option B

4. Quick Check:

   Default parameters = fallback values [OK]

Hint: Default values fill in missing arguments automatically [OK]

Common Mistakes:

• Thinking default values speed up code
• Believing default values force arguments
• Confusing default parameters with variable declarations

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

easy

A. func greet(name: String) { name = "Guest"; print("Hello, \(name)!") }

B. func greet(name: String) = "Guest" { print("Hello, \(name)!") }

C. func greet(name: String default "Guest") { print("Hello, \(name)!") }

D. func greet(name: String = "Guest") { print("Hello, \(name)!") }

Solution

1. Step 1: Review Swift default parameter syntax

   In Swift, default values are assigned using an equals sign after the parameter type.

2. Step 2: Check each option

   func greet(name: String = "Guest") { print("Hello, \(name)!") } uses correct syntax: name: String = "Guest". Others have syntax errors.

3. Final Answer:

   func greet(name: String = "Guest") { print("Hello, \(name)!") } -> Option D

4. Quick Check:

   Default parameter syntax = type = value [OK]

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

Common Mistakes:

• Placing default value outside parentheses
• Using = after parameter name without type
• Trying to assign default inside function body

3. What will be the output of this Swift code?

func multiply(_ a: Int, by b: Int = 2) -> Int {
    return a * b
}

print(multiply(5))

medium

A. Error: Missing argument for parameter 'b'

B. 5

C. 10

D. 25

Solution

1. Step 1: Understand function parameters

   The function multiply takes two parameters: 'a' and 'b' with a default value of 2.

2. Step 2: Evaluate the call multiply(5)

   Only 'a' is provided as 5, so 'b' uses default 2. Result is 5 * 2 = 10.

3. Final Answer:

   10 -> Option C

4. Quick Check:

   5 * default 2 = 10 [OK]

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

Common Mistakes:

• Expecting error for missing argument
• Using first argument for both parameters
• Confusing default value with multiplication factor

4. Identify the error in this Swift function declaration:

func greet(name: String = "User", _ age: Int) {
    print("Hello \(name), you are \(age) years old.")
}

medium

A. Default parameter must be last in the parameter list

B. Missing return type

C. Cannot use default values with String type

D. Function body syntax error

Solution

1. Step 1: Check parameter order rules

   In Swift, parameters with default values must come after parameters without defaults.

2. Step 2: Analyze given function

   'name' has a default but appears before 'age' which has no default. This causes a compile error.

3. Final Answer:

   Default parameter must be last in the parameter list -> Option A

4. Quick Check:

   Default params last = correct order [OK]

Hint: Place parameters with defaults after others [OK]

Common Mistakes:

• Putting default parameters before non-default ones
• Assuming return type is mandatory for void functions
• Confusing type restrictions on default values

5. You want to write a Swift function formatMessage that takes a text and an optional prefix with default value "Info:". It should return a string combining prefix and text separated by a space. Which is the correct function and call to get output "Info: Hello"?

hard

A. func formatMessage(text: String, prefix: String = "Info:") -> String { return "\(prefix) \(text)" }
print(formatMessage(text: "Hello"))

B. func formatMessage(prefix: String = "Info:", text: String) -> String { return "\(text) \(prefix)" }
print(formatMessage(text: "Hello"))

C. func formatMessage(text: String, prefix: String) -> String { return "\(prefix) \(text)" }
print(formatMessage(text: "Hello"))

D. func formatMessage(text: String, prefix: String = "Info:") -> String { return "\(text) \(prefix)" }
print(formatMessage(text: "Hello"))

Solution

1. Step 1: Define function with default parameter last

   Parameter with default 'prefix' must come after 'text' without default.

2. Step 2: Check function call and output

   Calling with only 'text' uses default prefix "Info:" and returns "Info: Hello".

3. Final Answer:

   func formatMessage(text: String, prefix: String = "Info:") -> String { return "\(prefix) \(text)" } print(formatMessage(text: "Hello")) -> Option A

4. Quick Check:

   Default param last + call with one arg = correct output [OK]

Hint: Default params last, call with missing arg uses default [OK]

Common Mistakes:

• Placing default parameter before non-default
• Calling function without required parameters
• Swapping order of prefix and text in output