Methods in structs in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a method named greet inside the struct.

Swift

struct Person {
    var name: String
    func [1]() {
        print("Hello, \(name)!")
    }
}

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

Agreeting

BsayHello

Chello

Dgreet

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name different from 'greet' will cause the method not to be recognized.

The method name should be greet as defined in the instruction.

2fill in blank

medium

Complete the code to call the greet method on the person instance.

Swift

var person = Person(name: "Anna")
person.[1]()

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

Agreet

BsayHello

Chello

Dgreeting

Attempts:

3 left

💡 Hint

Common Mistakes

Calling a method name that does not exist on the struct instance.

To call the method defined as greet, use person.greet().

3fill in blank

hard

Fix the error by completing the method signature to modify the struct's property.

Swift

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

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

Aincrement

Bincrease

CaddOne

Dmutate

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name that does not match the intended action.

The method name increment clearly indicates increasing the count by one.

4fill in blank

hard

Fill both blanks to create a method that returns a greeting with the person's name.

Swift

struct Person {
    var name: String
    func [1]() -> String {
        return "Hello, \([2])!"
    }
}

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

Agreet

Bname

CpersonName

DsayHello

Attempts:

3 left

💡 Hint

Common Mistakes

Using a property name that does not exist in the struct.

The method is named greet and it returns a string using the property name.

5fill in blank

hard

Fill all three blanks to define a mutating method that resets the count to zero and returns a message.

Swift

struct Counter {
    var count: Int
    mutating func [1]() -> String {
        count = [2]
        return "Count reset to [3]"
    }
}

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

Areset

B0

Czero

Dclear

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-mutating method to change a property.

The method named reset sets count to 0 and returns a message with the word 'zero'.

Practice

1.

What is the main purpose of a method inside a Swift struct?

easy

A. To define actions the struct can perform

B. To store data values

C. To create a new struct type

D. To import external libraries

Solution

1. Step 1: Understand what methods do in structs

   Methods are functions inside structs that define behaviors or actions the struct can perform.

2. Step 2: Differentiate methods from data storage

   Properties store data, while methods perform actions using that data.

3. Final Answer:

   To define actions the struct can perform -> Option A

4. Quick Check:

   Methods = actions in structs [OK]

Hint: Methods = actions inside structs, properties = data [OK]

Common Mistakes:

• Confusing methods with properties
• Thinking methods create new types
• Mixing methods with import statements

2.

Which keyword must be used before a method in a Swift struct if it changes the struct's properties?

easy

A. final

B. override

C. static

D. mutating

Solution

1. Step 1: Recall Swift's rule for modifying struct properties

   Struct methods that change properties must be marked with mutating to allow modification.

2. Step 2: Identify the correct keyword

   Among the options, only mutating enables property changes inside struct methods.

3. Final Answer:

   mutating -> Option D

4. Quick Check:

   Change properties = mutating [OK]

Hint: Use mutating for methods that change struct properties [OK]

Common Mistakes:

• Using override in structs (only for classes)
• Confusing static with mutating
• Omitting mutating keyword causes errors

3.

What will be the output of this Swift code?

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

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

medium

A. 0

B. 1

C. Error: Cannot modify property

D. nil

Solution

1. Step 1: Understand the mutating method increment()

   The method increases count by 1 and is marked mutating, so it can change the property.

2. Step 2: Trace the code execution

   myCounter starts with count = 0, increment() adds 1, so count becomes 1, then printed.

3. Final Answer:

   1 -> Option B

4. Quick Check:

   mutating method changes count to 1 [OK]

Hint: mutating methods can change properties, so count increments [OK]

Common Mistakes:

• Forgetting mutating causes error
• Expecting count to stay 0
• Thinking print outputs nil

4.

Identify the error in this Swift struct method and how to fix it:

struct Score {
    var points = 0
    func addPoint() {
        points += 1
    }
}

medium

A. Method should return points value

B. Property points must be let instead of var

C. Method must be marked mutating to change points

D. No error, code runs fine

Solution

1. Step 1: Check if method modifies a property

   addPoint() tries to increase points by 1, which modifies the struct's property.

2. Step 2: Recall Swift rule for modifying properties in structs

   Methods that modify properties must be marked mutating, otherwise compiler error occurs.

3. Final Answer:

   Method must be marked mutating to change points -> Option C

4. Quick Check:

   Modify property in struct method = mutating needed [OK]

Hint: Add mutating keyword to methods that change struct properties [OK]

Common Mistakes:

• Omitting mutating keyword
• Changing var to let (makes property immutable)
• Thinking method must return value

5.

Given this struct, which method correctly resets the level property to 1?

struct Game {
    var level = 5

    // Which method resets level to 1?
}

hard

A. mutating func reset() { level = 1 }

B. mutating func reset() -> Int { return 1 }

C. static func reset() { level = 1 }

D. func reset() { level = 1 }

Solution

1. Step 1: Identify method that changes a property

   Resetting level means changing the property, so method must be mutating.

2. Step 2: Check each option

   A lacks mutating, so cannot modify property. B is mutating but only returns 1 without changing level. C is static and cannot access instance property. D is mutating and correctly sets level to 1.

3. Final Answer:

   mutating func reset() { level = 1 } -> Option A

4. Quick Check:

   Change property in struct method = mutating func [OK]

Hint: Use mutating func to change struct properties inside methods [OK]

Common Mistakes:

• Forgetting mutating keyword
• Using static func to access instance properties
• Returning value instead of changing property