Adding methods in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Swift code with a method?

Consider this Swift struct with a method. What will be printed when the code runs?

Swift

struct Counter {
    var count = 0
    mutating func increment() {
        count += 1
    }
}

var myCounter = Counter()
myCounter.increment()
print(myCounter.count)

A Compilation error: cannot use mutating method on variable

B 1

C 0

D Runtime error

💡 Hint

Remember that mutating methods can change properties of structs when called on variables.

The method increment() increases count by 1. Since myCounter is a variable (var), calling increment() works and count becomes 1.

❓ Predict Output

intermediate

What does this class method print?

Look at this Swift class with a method. What will be printed when the code runs?

Swift

class Greeter {
    func greet() {
        print("Hello, Swift!")
    }
}

let greeter = Greeter()
greeter.greet()

A Compilation error: cannot call method on constant

B No output

C Runtime error: method not found

D Hello, Swift!

💡 Hint

Classes allow methods to be called on instances even if the instance is a constant.

The greet() method prints "Hello, Swift!". Calling it on greeter prints this message.

🔧 Debug

advanced

Why does this Swift code cause a compile error?

This Swift struct has a method that tries to modify a property but causes a compile error. Why?

Swift

struct Point {
    var x = 0
    var y = 0
    mutating func moveBy(dx: Int, dy: Int) {
        x += dx
        y += dy
    }
}

A Because moveBy is not marked as mutating, so it cannot change properties

B Because x and y are constants and cannot be changed

C Because structs cannot have methods

D Because dx and dy parameters are constants

💡 Hint

In Swift, methods that change properties of structs must be marked mutating.

The method moveBy tries to change x and y but is not marked mutating, so the compiler disallows it.

❓ Predict Output

advanced

What is the output of this Swift code with a static method?

Look at this Swift class with a static method. What will be printed when the code runs?

Swift

class MathHelper {
    static func square(_ number: Int) -> Int {
        return number * number
    }
}

print(MathHelper.square(5))

A Compilation error: cannot call static method like this

B 5

C 25

D Runtime error

💡 Hint

Static methods belong to the type itself and can be called without creating an instance.

The static method square returns the number multiplied by itself. Calling square(5) returns 25.

🧠 Conceptual

expert

Which statement about methods in Swift is true?

Choose the correct statement about methods in Swift.

A Mutating methods can modify properties of value types like structs and enums

B Instance methods cannot access properties of the instance

C Static methods can only be called on instances, not on the type itself

D Only classes can have methods; structs and enums cannot

💡 Hint

Think about how value types like structs behave when methods change their properties.

Mutating methods allow structs and enums to modify their own properties. Classes do not need mutating because they are reference types.