Variadic parameters in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a function that accepts a variable number of integers.

Swift

func sum(numbers: [1]) -> Int {
    return numbers.reduce(0, +)
}

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

A...

B...Int

C...Ints

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the three dots (...) before the type.

Using plural forms like Ints which is invalid syntax.

The ...Int syntax defines a variadic parameter that accepts zero or more integers.

2fill in blank

medium

Complete the code to call the variadic function with three integer arguments.

Swift

let result = sum(numbers: [1])

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

A1, 2, 3

B[1, 2, 3]

C(1, 2, 3)

D"1, 2, 3"

Attempts:

3 left

💡 Hint

Common Mistakes

Passing an array instead of comma-separated values.

Passing a tuple or string instead of separate values.

Variadic parameters are passed as comma-separated values, not as arrays or tuples.

3fill in blank

hard

Fix the error in the function definition to correctly accept a variable number of strings.

Swift

func greet(names: [1]) {
    for name in names {
        print("Hello, \(name)!")
    }
}

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

A...Strings

B...

C...String

Attempts:

3 left

💡 Hint

Common Mistakes

Using plural type names like Strings.

Omitting the three dots.

The correct syntax for variadic parameters requires three dots before the type, like ...String.

4fill in blank

hard

Fill both blanks to create a function that returns the average of a variable number of Double values.

Swift

func average(values: [1]) -> Double {
    let total = values[2]reduce(0.0, +)
    return total / Double(values.count)
}

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

A...

B...Double

C.

D?

Attempts:

3 left

💡 Hint

Common Mistakes

Using a question mark instead of a dot before reduce.

Omitting the three dots in the parameter.

The variadic parameter uses ...Double. To call reduce on the array, use the dot operator ..

5fill in blank

hard

Fill all three blanks to define and call a function that prints all provided strings separated by commas.

Swift

func printAll(items: [1]) {
    let combined = items[2]joined(separator: [3])
    print(combined)
}

printAll(items: "apple", "banana", "cherry")

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

A...String

B.

C", "

D...

Attempts:

3 left

💡 Hint

Common Mistakes

Using '...' instead of '...String' in the parameter.

Forgetting the dot before joined.

Using wrong separator string.

The function uses ...String for variadic parameters. The joined(separator:) method is called with a dot and a string separator ", ".

Practice

1. What does a variadic parameter in Swift allow a function to do?

easy

A. Limit the number of arguments to exactly two

B. Accept any number of values of the same type

C. Accept only one value of any type

D. Return multiple values from a function

Solution

1. Step 1: Understand variadic parameter purpose

   Variadic parameters let a function accept zero or more values of the same type.

2. Step 2: Compare options with definition

   Only Accept any number of values of the same type correctly describes this behavior.

3. Final Answer:

   Accept any number of values of the same type -> Option B

4. Quick Check:

   Variadic parameter = multiple values [OK]

Hint: Variadic means 'variable number' of same type values [OK]

Common Mistakes:

• Confusing variadic with multiple return values
• Thinking it accepts different types
• Assuming it limits arguments

2. Which of the following is the correct way to declare a variadic parameter in Swift?

easy

A. func sum(numbers: Int*) { }

B. func sum(numbers: [Int]) { }

C. func sum(numbers: Int...) { }

D. func sum(numbers: Int) { }

Solution

1. Step 1: Recall variadic syntax in Swift

   Variadic parameters use three dots (...) after the type.

2. Step 2: Check each option

   func sum(numbers: Int...) { } uses 'Int...' which is correct syntax for variadic parameters.

3. Final Answer:

   func sum(numbers: Int...) { } -> Option C

4. Quick Check:

   Variadic syntax = Type... [OK]

Hint: Look for three dots (...) after type for variadic [OK]

Common Mistakes:

• Using asterisk (*) instead of three dots
• Using array type instead of variadic
• Missing dots after type

3. What is the output of this Swift code?

func greet(names: String...) {
    for name in names {
        print("Hello, \(name)!")
    }
}
greet(names: "Anna", "Bob")

medium

A. Hello, Anna!\nHello, Bob!

B. Hello, names!

C. Hello, Anna, Bob!

D. Error: Cannot use variadic parameter here

Solution

1. Step 1: Understand variadic parameter behavior

   The parameter 'names' collects all arguments into an array of strings.

2. Step 2: Trace the for loop output

   The loop prints "Hello, Anna!" and then "Hello, Bob!" each on a new line.

3. Final Answer:

   Hello, Anna!\nHello, Bob! -> Option A

4. Quick Check:

   Variadic parameter prints each argument separately [OK]

Hint: Variadic acts like array; loop prints each item [OK]

Common Mistakes:

• Thinking it prints all names in one line
• Assuming a syntax error
• Confusing parameter name with output

4. Identify the error in this Swift function using variadic parameters:

func multiply(numbers: Int...) -> Int {
    var result = 1
    for i in 0..

medium

A. The for loop syntax is incorrect

B. Missing return statement in function

C. Variadic parameters cannot be used with Int type

D. Calling multiply without any arguments causes an error

Solution

1. Step 1: Analyze function call

   The call 'multiply(numbers: )' passes no arguments, which is allowed but syntax requires no empty parentheses.

2. Step 2: Understand Swift call syntax for variadic

   Calling with empty parentheses after variadic parameter name is invalid; omit arguments or provide values.

3. Final Answer:

   Calling multiply without any arguments causes an error -> Option D

4. Quick Check:

   Empty variadic call syntax invalid [OK]

Hint: Call variadic with values or omit parentheses if none [OK]

Common Mistakes:

• Thinking for loop is wrong
• Believing Int can't be variadic
• Missing return statement error

5. How can you write a Swift function that accepts any number of integers and returns their average as a Double using variadic parameters?

hard

A. func average(numbers: Int...) -> Double { Double(numbers.reduce(0, +)) / Double(numbers.count) }

B. func average(numbers: [Int]) -> Double { Double(numbers.reduce(0, +)) / Double(numbers.count) }

C. func average(numbers: Int...) -> Int { numbers.reduce(0, +) / numbers.count }

D. func average(numbers: Int*) -> Double { Double(numbers.reduce(0, +)) / Double(numbers.count) }

Solution

1. Step 1: Use variadic parameter syntax

   func average(numbers: Int...) -> Double { Double(numbers.reduce(0, +)) / Double(numbers.count) } correctly uses 'Int...' to accept any number of integers.

2. Step 2: Calculate average as Double

   It sums all numbers and divides by count, converting to Double for decimal average.

3. Final Answer:

   func average(numbers: Int...) -> Double { Double(numbers.reduce(0, +)) / Double(numbers.count) } -> Option A

4. Quick Check:

   Variadic + Double average calculation = func average(numbers: Int...) -> Double { Double(numbers.reduce(0, +)) / Double(numbers.count) } [OK]

Hint: Use Int... and convert sum/count to Double for average [OK]

Common Mistakes:

• Using array instead of variadic parameter
• Returning Int instead of Double for average
• Using invalid syntax like Int*