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.

Practice

1. What is the purpose of an argument label in a Swift function?

easy

A. To store the return value of the function

B. To define the variable type inside the function

C. To clarify the meaning of each argument when calling the function

D. To create a new function inside another function

Solution

1. Step 1: Understand argument labels

   Argument labels are used outside the function when calling it to make the call clearer.

2. Step 2: Differentiate from parameter names

   Parameter names are used inside the function, but argument labels help the caller understand what each value means.

3. Final Answer:

   To clarify the meaning of each argument when calling the function -> Option C

4. Quick Check:

   Argument label = clarify call [OK]

Hint: Argument labels clarify calls, parameter names work inside [OK]

Common Mistakes:

• Confusing argument labels with parameter names
• Thinking argument labels define variable types
• Assuming argument labels store return values

2. Which of the following is the correct way to declare a function with an argument label from and a parameter name start of type Int?

easy

A. func move(from: start Int) { }

B. func move(from start: Int) { }

C. func move(start from: Int) { }

D. func move(Int from start) { }

Solution

1. Step 1: Recall Swift function syntax for labels

   The syntax is: func name(argumentLabel parameterName: Type) { }.

2. Step 2: Match the syntax with given options

   func move(from start: Int) { } matches this syntax exactly: func move(from start: Int) { }.

3. Final Answer:

   func move(from start: Int) { } -> Option B

4. Quick Check:

   Argument label before parameter name [OK]

Hint: Argument label comes before parameter name in declaration [OK]

Common Mistakes:

• Swapping argument label and parameter name order
• Putting type before parameter name
• Using invalid syntax with colons misplaced

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

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

medium

A. Hello, Anna!

B. Error: Missing argument label

C. Hello, name!

D. Hello, person!

Solution

1. Step 1: Understand argument label and parameter name

   The function uses argument label person and parameter name name. The call uses person: "Anna".

2. Step 2: Check the print statement

   Inside the function, name is used, so it prints "Hello, Anna!".

3. Final Answer:

   Hello, Anna! -> Option A

4. Quick Check:

   Argument label person calls parameter name name [OK]

Hint: Argument label used in call, parameter name used inside function [OK]

Common Mistakes:

• Confusing argument label with parameter name in print
• Calling function without argument label
• Expecting argument label to print

4. Identify the error in this Swift function call:

func calculate(sum total: Int) {
    print(total)
}
calculate(5)

medium

A. Parameter name 'total' is incorrect

B. The print statement is invalid

C. Function should return a value

D. Missing argument label 'sum' in the function call

Solution

1. Step 1: Check function declaration

   The function requires an argument label sum when called.

2. Step 2: Check function call

   The call calculate(5) misses the argument label sum, so it causes an error.

3. Final Answer:

   Missing argument label 'sum' in the function call -> Option D

4. Quick Check:

   Argument label required in call [OK]

Hint: Always use argument labels in calls if declared [OK]

Common Mistakes:

• Omitting argument labels in function calls
• Confusing parameter names with argument labels
• Expecting implicit argument labels

5. Given the function:

func update(user name: String, age years: Int) {
    print("User: \(name), Age: \(years)")
}

Which is the correct way to call this function to print User: John, Age: 30?

hard

A. update(user: "John", age: 30)

B. update(name: "John", years: 30)

C. update(user name: "John", age years: 30)

D. update("John", 30)

Solution

1. Step 1: Identify argument labels and parameter names

   The function has argument labels user and age, with parameter names name and years.

2. Step 2: Match call syntax

   The call must use argument labels: update(user: "John", age: 30) is correct.

3. Final Answer:

   update(user: "John", age: 30) -> Option A

4. Quick Check:

   Call uses argument labels, function uses parameter names inside [OK]

Hint: Use argument labels in call, parameter names inside function [OK]

Common Mistakes:

• Using parameter names instead of argument labels in call
• Trying to call with both labels and names together
• Omitting argument labels entirely