Adding computed properties in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a computed property that returns the full name.

Swift

struct Person {
    var firstName: String
    var lastName: String
    var fullName: String {
        return firstName [1] lastName
    }
}

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

A+ " " +

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using arithmetic operators like '-' or '*' instead of '+' for strings.

Forgetting to add a space between first and last names.

The computed property fullName combines firstName and lastName with a space in between using the + operator.

2fill in blank

medium

Complete the code to add a computed property that calculates the area of a rectangle.

Swift

struct Rectangle {
    var width: Double
    var height: Double
    var area: Double {
        return width [1] height
    }
}

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

A-

B+

C/

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition instead of multiplication.

Using division or subtraction which are incorrect for area calculation.

The computed property area multiplies width and height to calculate the rectangle's area.

3fill in blank

hard

Fix the error in the computed property that returns the age in months.

Swift

struct Person {
    var ageInYears: Int
    var ageInMonths: Int {
        return ageInYears [1] 12
    }
}

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

A+

B*

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition instead of multiplication.

Using division which would give incorrect results.

To convert years to months, multiply the age in years by 12.

4fill in blank

hard

Fill both blanks to create a computed property that returns the perimeter of a rectangle.

Swift

struct Rectangle {
    var width: Double
    var height: Double
    var perimeter: Double {
        return (width [1] height) [2] 2
    }
}

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

A+

B*

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Multiplying width and height instead of adding.

Forgetting to multiply the sum by 2.

The perimeter of a rectangle is 2 times the sum of width and height. So first add width and height, then multiply by 2.

5fill in blank

hard

Fill all three blanks to create a computed property that returns the initials of a person.

Swift

struct Person {
    var firstName: String
    var lastName: String
    var initials: String {
        return firstName[1].uppercased() [2] lastName[3].uppercased()
    }
}

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

A[first]

B+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction instead of addition to join strings.

Not using subscript to get the first character.

Not converting characters to uppercase.

The computed property initials takes the first character of firstName and lastName, converts them to uppercase, and joins them with +.

Practice

1. What is a computed property in Swift?

easy

A. A property that calculates a value instead of storing it.

B. A property that stores a fixed value only.

C. A property that can only be set once.

D. A property that is always optional.

Solution

1. Step 1: Understand property types in Swift

   Stored properties hold data directly, while computed properties calculate values when accessed.

2. Step 2: Identify computed property behavior

   Computed properties use get (and optionally set) to calculate values dynamically instead of storing them.

3. Final Answer:

   A property that calculates a value instead of storing it. -> Option A

4. Quick Check:

   Computed property = calculates value [OK]

Hint: Computed properties calculate values on demand, not store them [OK]

Common Mistakes:

• Confusing computed properties with stored properties
• Thinking computed properties always store data
• Assuming computed properties cannot have setters

2. Which of the following is the correct syntax to add a computed property area to a struct Square that returns side * side?

easy

A. func area() -> Int { side * side }

B. var area: Int { return side * side }

C. var area: Int = side * side

D. let area = side * side

Solution

1. Step 1: Recognize computed property syntax

   Computed properties use curly braces with a get block or implicit return inside braces.

2. Step 2: Match syntax to the options

   var area: Int { return side * side } uses var area: Int { return side * side }, which is correct for a computed property. var area: Int = side * side tries to assign directly, which is invalid for computed properties.

3. Final Answer:

   var area: Int { return side * side } -> Option B

4. Quick Check:

   Computed property syntax = var name: Type { return value } [OK]

Hint: Use braces and return for computed properties, not direct assignment [OK]

Common Mistakes:

• Using '=' instead of braces for computed properties
• Defining computed property as a function
• Using 'let' instead of 'var' for computed properties

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

struct Circle {
    var radius: Double
    var diameter: Double {
        get { radius * 2 }
        set { radius = newValue / 2 }
    }
}

var c = Circle(radius: 5)
c.diameter = 20
print(c.radius)

medium

A. 5.0

B. Syntax error

C. 20.0

D. 10.0

Solution

1. Step 1: Understand the computed property setter

   Setting c.diameter = 20 triggers the set block, which sets radius = newValue / 2. So radius becomes 20 / 2 = 10.

2. Step 2: Print the updated radius

   After setting diameter, printing c.radius outputs 10.0.

3. Final Answer:

   10.0 -> Option D

4. Quick Check:

   Setter updates radius to 10.0 [OK]

Hint: Setter changes radius to half the diameter value [OK]

Common Mistakes:

• Ignoring the setter and expecting radius unchanged
• Confusing diameter and radius values
• Assuming syntax error due to setter

4. Identify the error in this computed property code:

struct Rectangle {
    var width: Double
    var height: Double
    var area: Double {
        get { width * height }
        set { width = newValue / height }
    }
}

medium

A. width and height must be constants (let).

B. Getter must have parentheses after width * height.

C. Setter can cause division by zero if height is zero.

D. Computed properties cannot have setters.

Solution

1. Step 1: Analyze the setter logic

   The setter divides newValue by height. If height is zero, this causes a runtime error (division by zero).

2. Step 2: Check other options

   Getter syntax is correct without parentheses. Computed properties can have setters. Variables can be var. So only the setter can cause division by zero if height is zero.

3. Final Answer:

   Setter can cause division by zero if height is zero. -> Option C

4. Quick Check:

   Division by zero risk in setter = Setter can cause division by zero if height is zero. [OK]

Hint: Check for zero in divisor inside setter to avoid runtime errors [OK]

Common Mistakes:

• Thinking getter needs parentheses
• Believing computed properties can't have setters
• Assuming width and height must be constants

5. You want to add a computed property fullName to this struct that combines firstName and lastName with a space, and also allows setting both names by splitting the input string. Which code correctly implements this?

struct Person {
    var firstName: String
    var lastName: String
    // Add fullName computed property here
}

hard

A. var fullName: String {
get { "\(firstName) \(lastName)" }
set {
let parts = newValue.split(separator: " ")
if parts.count == 2 {
firstName = String(parts[0])
lastName = String(parts[1])
}
}
}

B. var fullName: String {
return "\(firstName) \(lastName)"
}

C. var fullName: String {
get { firstName + lastName }
set { firstName = newValue }
}

D. var fullName: String = ""

Solution

1. Step 1: Understand the requirements

   The computed property must combine first and last names with a space in the getter, and split the input string to set both names in the setter.

2. Step 2: Evaluate each option

   var fullName: String { get { "\(firstName) \(lastName)" } set { let parts = newValue.split(separator: " ") if parts.count == 2 { firstName = String(parts[0]) lastName = String(parts[1]) } } } correctly implements a getter returning "firstName lastName" and a setter splitting the input string into two parts to assign firstName and lastName. var fullName: String { return "\(firstName) \(lastName)" } lacks a setter. var fullName: String { get { firstName + lastName } set { firstName = newValue } } concatenates without space and sets only firstName. var fullName: String = "" is a stored property, not computed.

3. Final Answer:

   var fullName: String { get { "\(firstName) \(lastName)" } set { let parts = newValue.split(separator: " ") if parts.count == 2 { firstName = String(parts[0]) lastName = String(parts[1]) } } } -> Option A

4. Quick Check:

   Computed property with get and set splitting string = var fullName: String { get { "\(firstName) \(lastName)" } set { let parts = newValue.split(separator: " ") if parts.count == 2 { firstName = String(parts[0]) lastName = String(parts[1]) } } } [OK]

Hint: Use get for combining and set for splitting names [OK]

Common Mistakes:

• Omitting the setter for fullName
• Not splitting the input string correctly
• Using stored property instead of computed