Function declaration syntax in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple Swift function

What is the output of this Swift code?

Swift

func greet(name: String) -> String {
    return "Hello, \(name)!"
}

print(greet(name: "Anna"))

A greet(name: "Anna")

B Error: Missing return statement

C Hello, name!

D Hello, Anna!

💡 Hint

Look at how the function returns a string with the name inserted.

The function greet takes a string parameter and returns a greeting with that name. The print statement outputs the returned string.

❓ Predict Output

intermediate

Function with multiple parameters

What does this Swift function print?

Swift

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

print(multiply(3, 4))

A 7

B 12

C 34

D Error: Missing argument labels

💡 Hint

The function multiplies two numbers and returns the result.

The function multiply takes two integers without argument labels and returns their product. 3 times 4 is 12.

❓ Predict Output

advanced

Function with default parameter values

What is the output of this Swift code?

Swift

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

greet()
greet(name: "Sam")

A Welcome, Guest!\nWelcome, Sam!

B Welcome, !\nWelcome, Sam!

C Welcome, Guest!\nWelcome, Guest!

D Error: Missing argument for parameter 'name'

💡 Hint

Default parameters are used when no argument is provided.

The first call uses the default value "Guest". The second call uses the provided argument "Sam".

❓ Predict Output

advanced

Function with inout parameter

What is the value of x after this Swift code runs?

Swift

func increment(value: inout Int) {
    value += 1
}

var x = 5
increment(value: &x)
x

A 6

B Error: Cannot pass immutable value as inout argument

C 5

D Error: Missing & before argument

💡 Hint

inout allows the function to modify the original variable.

The function increments the value by 1. Passing x with & allows the change to affect x itself.

❓ Predict Output

expert

Function with multiple return values using tuple

What does this Swift code print?

Swift

func minMax(numbers: [Int]) -> (min: Int, max: Int)? {
    guard !numbers.isEmpty else { return nil }
    var currentMin = numbers[0]
    var currentMax = numbers[0]
    for number in numbers[1...] {
        if number < currentMin {
            currentMin = number
        } else if number > currentMax {
            currentMax = number
        }
    }
    return (currentMin, currentMax)
}

if let result = minMax(numbers: [3, 7, 2, 9, 4]) {
    print("Min is \(result.min), Max is \(result.max)")
} else {
    print("Empty array")
}

A Min is 9, Max is 2

B Min is 3, Max is 7

C Min is 2, Max is 9

D Empty array

💡 Hint

The function finds the smallest and largest numbers in the array.

The function returns a tuple with the minimum and maximum values. The array contains 2 as smallest and 9 as largest.

Practice

1. Which keyword is used to declare a function in Swift?

easy

A. def

B. func

C. function

D. method

Solution

1. Step 1: Recall Swift function declaration

   In Swift, functions always start with the keyword func.

2. Step 2: Compare options

   Only func uses func, the correct keyword for Swift functions.

3. Final Answer:

   func -> Option B

4. Quick Check:

   Swift functions start with func [OK]

Hint: Remember: Swift functions always start with 'func' keyword [OK]

Common Mistakes:

• Using 'function' instead of 'func'
• Confusing Swift with Python's 'def'
• Using 'method' which is not a keyword

2. Which of the following is the correct syntax to declare a function named greet that takes no parameters and returns nothing?

easy

A. func greet() -> void {}

B. function greet() {}

C. func greet {}

D. func greet() {}

Solution

1. Step 1: Check function declaration syntax

   In Swift, a function with no parameters and no return type is declared as func name() {}.

2. Step 2: Analyze each option

   func greet() {} matches the correct syntax. function greet() {} uses 'function' which is invalid. func greet {} misses parentheses. func greet() -> void {} uses 'void' which is not used in Swift.

3. Final Answer:

   func greet() {} -> Option D

4. Quick Check:

   Empty parameter list needs () and no return type means no arrow [OK]

Hint: Empty parameters always need () after function name [OK]

Common Mistakes:

• Omitting parentheses for parameters
• Using 'function' instead of 'func'
• Using 'void' as return type in Swift

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

func add(a: Int, b: Int) -> Int {
    return a + b
}

print(add(a: 3, b: 4))

medium

A. a + b

B. 34

C. 7

D. Error: Missing return statement

Solution

1. Step 1: Understand function parameters and return

   The function add takes two integers and returns their sum.

2. Step 2: Calculate the function call result

   Calling add(a: 3, b: 4) returns 3 + 4 = 7, which is printed.

3. Final Answer:

   7 -> Option C

4. Quick Check:

   Sum of 3 and 4 is 7 [OK]

Hint: Add numbers inside function and print result [OK]

Common Mistakes:

• Concatenating numbers as strings
• Forgetting to return a value
• Misunderstanding parameter labels

4. Identify the error in the following Swift function declaration:

func multiply(a: Int, b Int) -> Int {
    return a * b
}

medium

A. Missing colon between parameter name and type for b

B. Missing return keyword

C. Function name is invalid

D. Return type should be String

Solution

1. Step 1: Check parameter syntax

   Each parameter must have a colon between its name and type. Here, b Int is missing a colon.

2. Step 2: Confirm other parts are correct

   The return keyword is present, function name is valid, and return type Int is appropriate.

3. Final Answer:

   Missing colon between parameter name and type for b -> Option A

4. Quick Check:

   Parameters need colon between name and type [OK]

Hint: Check colons between parameter names and types [OK]

Common Mistakes:

• Omitting colon in parameter list
• Forgetting return keyword
• Using wrong return type

5. You want to declare a Swift function named describePerson that takes a String parameter name and an Int parameter age, and returns a String describing the person like "Name is Age years old." Which is the correct function declaration?

hard

A. func describePerson(name: String, age: Int) -> String {
return "\(name) is \(age) years old."
}

B. func describePerson(name String, age Int) -> String {
return "\(name) is \(age) years old."
}

C. func describePerson(name: String, age: Int) {
print("\(name) is \(age) years old.")
}

D. func describePerson(name: String, age: Int) -> Void {
return "\(name) is \(age) years old."
}

Solution

1. Step 1: Check parameter syntax and return type

   Parameters must have colons between name and type. The function returns a String, so return type must be String.

2. Step 2: Verify function body matches return type

   func describePerson(name: String, age: Int) -> String { return "\(name) is \(age) years old." } returns a String with correct string interpolation. func describePerson(name String, age Int) -> String { return "\(name) is \(age) years old." } misses colons. func describePerson(name: String, age: Int) { print("\(name) is \(age) years old.") } has no return type and uses print instead of return. func describePerson(name: String, age: Int) -> Void { return "\(name) is \(age) years old." } uses Void return type but returns a String, which is invalid.

3. Final Answer:

   func describePerson(name: String, age: Int) -> String { return "\(name) is \(age) years old." } -> Option A

4. Quick Check:

   Correct parameters and return type with string interpolation [OK]

Hint: Use colons for parameters and match return type with returned value [OK]

Common Mistakes:

• Omitting colons in parameters
• Using print instead of return for returning values
• Mismatching return type and returned value