Variadic parameters in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a variadic sum function

What is the output of this Swift code that uses a variadic parameter to sum numbers?

Swift

func sum(_ numbers: Int...) -> Int {
    var total = 0
    for number in numbers {
        total += number
    }
    return total
}

print(sum(1, 2, 3, 4))

A 0

B 1234

C 10

D Error: variadic parameters cannot be used this way

💡 Hint

Think about how the function adds all the numbers passed in.

The function sum takes any number of Int values and adds them all together. The call sum(1, 2, 3, 4) returns 10.

❓ Predict Output

intermediate

Variadic parameters with no arguments

What will this Swift code print when calling a variadic function with no arguments?

Swift

func greet(names: String...) {
    print("Hello, \(names.count) people!")
}

greet()

A Compile error: missing arguments

B Hello, 1 people!

C Hello, nil people!

D Hello, 0 people!

💡 Hint

Variadic parameters can be empty, so count will be zero.

Calling greet() with no arguments means names is an empty array, so names.count is 0.

🧠 Conceptual

advanced

Understanding variadic parameter restrictions

Which statement about variadic parameters in Swift is true?

A Variadic parameters must be the last parameter in the function signature.

B A function can have multiple variadic parameters.

C Variadic parameters can only accept Int values.

D Variadic parameters automatically unwrap optional values.

💡 Hint

Think about the position of variadic parameters in function definitions.

Swift requires that variadic parameters be the last parameter in the function signature. Only one variadic parameter is allowed.

❓ Predict Output

advanced

Output of variadic function with mixed parameter types

What is the output of this Swift code using a variadic parameter and a normal parameter?

Swift

func describe(age: Int, hobbies: String...) {
    print("Age: \(age)")
    print("Hobbies count: \(hobbies.count)")
    for hobby in hobbies {
        print(hobby)
    }
}

describe(age: 30, hobbies: "Reading", "Swimming")

A

Age: 30
Hobbies count: 0

B

Age: 30
Hobbies count: 2
Reading
Swimming

C

Age: 30
Hobbies count: 1
Reading, Swimming

D Compile error: variadic parameter must be last

💡 Hint

Check how many hobbies are passed and printed.

The function prints the age, then the count of hobbies (2), then each hobby on its own line.

❓ Predict Output

expert

Result of passing an array to a variadic parameter

What will this Swift code print when passing an array to a variadic parameter using the spread operator?

Swift

func multiply(factor: Int, numbers: Int...) -> [Int] {
    numbers.map { $0 * factor }
}

let values = [1, 2, 3]
let result = multiply(factor: 2, numbers: values...)
print(result)

A [2, 4, 6]

B [1, 2, 3, 2]

C [4, 6, 8]

D Error: cannot use '...' to expand array here

💡 Hint

The '...' operator expands the array elements as separate arguments.

The array values is expanded into separate arguments 1, 2, 3 for the variadic parameter. Each is multiplied by 2.