Argument labels and parameter names in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of function call with argument labels

What is the output of this Swift code?

Swift

func greet(person name: String) {
    print("Hello, \(name)!")
}
greet(person: "Anna")

A Hello, name!

B Hello, person!

C Error: Missing argument label

D Hello, Anna!

💡 Hint

Check how the argument label and parameter name are used in the function call.

The function greet uses 'person' as the argument label and 'name' as the parameter name. Calling greet(person: "Anna") passes "Anna" to the parameter 'name', so it prints "Hello, Anna!".

❓ Predict Output

intermediate

Result of function with omitted argument label

What will this Swift code print?

Swift

func multiply(_ a: Int, by b: Int) -> Int {
    return a * b
}
print(multiply(3, by: 4))

A Error: Missing argument label for first parameter

B 7

C 12

D Error: Missing argument label for second parameter

💡 Hint

The underscore (_) means the first argument label is omitted.

The first parameter has an underscore, so no label is needed when calling. The second parameter requires the label 'by'. The call multiply(3, by: 4) returns 12.

🔧 Debug

advanced

Identify the error in function call with argument labels

Why does this Swift code cause an error?

Swift

func divide(_ numerator: Int, denominator: Int) -> Int {
    return numerator / denominator
}
divide(numerator: 10, denominator: 2)

A Error: Unexpected argument label for first parameter

B Error: Missing argument label for second parameter

C No error, output is 5

D Error: Cannot divide by zero

💡 Hint

Check the function definition and how the first parameter is called.

The first parameter has an underscore, so it must be called without a label. Calling divide(numerator: 10, denominator: 2) causes an error because 'numerator:' label is unexpected.

❓ Predict Output

advanced

Output of function with different argument labels and parameter names

What does this Swift code print?

Swift

func describe(person name: String, from city: String) {
    print("\(name) is from \(city).")
}
describe(person: "Liam", from: "Paris")

A Liam is from Paris.

B person is from city.

C Error: Missing argument label

D Liam is from from.

💡 Hint

Look at how argument labels and parameter names are used in the function call.

The function uses 'person' and 'from' as argument labels, and 'name' and 'city' as parameter names. The call matches the labels, so it prints 'Liam is from Paris.'.

🧠 Conceptual

expert

Understanding argument labels and parameter names in Swift

Which statement about argument labels and parameter names in Swift is correct?

A Parameter names are used only when calling the function.

B Argument labels appear in function calls, parameter names appear inside the function.

C Argument labels are used inside the function body to refer to parameters.

D You cannot omit argument labels in Swift functions.

💡 Hint

Think about the difference between how you call a function and how you write its code.

In Swift, argument labels are used when calling a function to clarify the meaning of each argument. Parameter names are used inside the function body to refer to those arguments.