Enum declaration and cases in Swift - Mini Project: Build & Apply

Enum declaration and cases

📖 Scenario: You are creating a simple app that tracks the weather condition for the day. You want to use an enum to represent different weather types.

🎯 Goal: Build a Swift program that declares an enum called Weather with specific cases, then prints a message based on a selected weather case.

📋 What You'll Learn

Declare an enum named Weather with cases sunny, rainy, and cloudy

Create a variable named todayWeather and assign it the sunny case of Weather

Use a switch statement on todayWeather to print a message for each weather case

Print the message to the console

💡 Why This Matters

🌍 Real World

Enums help represent fixed sets of related values, like weather types, user roles, or app states, making code easier to read and maintain.

💼 Career

Understanding enums is essential for Swift developers building iOS apps, as they are used widely for managing states and options clearly.

1

Declare the enum with weather cases

Declare an enum named Weather with these exact cases: sunny, rainy, and cloudy.

Swift

# Declare the enum Weather with cases sunny, rainy, and cloudy
// Your code here

Hint

Use the enum keyword followed by the name Weather. Inside curly braces, list each case with the case keyword.

2

Create a variable for today's weather

Create a variable named todayWeather and assign it the sunny case of the Weather enum.

Swift

enum Weather {
    case sunny
    case rainy
    case cloudy
}

// Create variable todayWeather and assign it Weather.sunny
// Your code here

Hint

Use var todayWeather = Weather.sunny to create and assign the variable.

3

Use a switch statement to handle weather cases

Write a switch statement on todayWeather with cases .sunny, .rainy, and .cloudy. For each case, assign a message string describing the weather to a variable named message. Use these exact messages: "It's a bright sunny day!", "Don't forget your umbrella.", and "Looks a bit cloudy today." respectively.

Swift

enum Weather {
    case sunny
    case rainy
    case cloudy
}

var todayWeather = Weather.sunny

// Use switch on todayWeather to assign message
// Your code here

Hint

Use switch todayWeather { case .sunny: ... } and assign the exact messages to message.

4

Print the weather message

Write a print statement to display the message variable.

Swift

enum Weather {
    case sunny
    case rainy
    case cloudy
}

var todayWeather = Weather.sunny

var message = ""
switch todayWeather {
case .sunny:
    message = "It's a bright sunny day!"
case .rainy:
    message = "Don't forget your umbrella."
case .cloudy:
    message = "Looks a bit cloudy today."
}

// Print the message
// Your code here

Hint

Use print(message) to show the message on the screen.

Practice

1. What is the purpose of an enum in Swift?

easy

A. To group related values under one name

B. To create a function

C. To declare a variable

D. To write a loop

Solution

1. Step 1: Understand what enums represent

   Enums group related values together to make code clearer and safer.

2. Step 2: Compare options with enum purpose

   Only To group related values under one name correctly describes grouping related values under one name.

3. Final Answer:

   To group related values under one name -> Option A

4. Quick Check:

   Enum purpose = Group related values [OK]

Hint: Enums group related values clearly and safely [OK]

Common Mistakes:

• Confusing enums with functions
• Thinking enums declare variables
• Mixing enums with loops

2. Which of the following is the correct way to declare an enum named Direction with cases north, south, east, and west?

easy

A. enum Direction = { north, south, east, west }

B. enum Direction: north, south, east, west {}

C. enum Direction { case north, south, east, west }

D. enum Direction { north; south; east; west }

Solution

1. Step 1: Recall Swift enum syntax

   Enums use the keyword enum, followed by the name and curly braces containing case declarations separated by commas.

2. Step 2: Check each option's syntax

   enum Direction { case north, south, east, west } uses correct syntax: enum Direction { case north, south, east, west }. Others use invalid syntax.

3. Final Answer:

   enum Direction { case north, south, east, west } -> Option C

4. Quick Check:

   Correct enum syntax = enum Direction { case north, south, east, west } [OK]

Hint: Use 'case' keyword with comma-separated values inside braces [OK]

Common Mistakes:

• Using '=' instead of braces
• Omitting 'case' keyword
• Separating cases with semicolons

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

enum Light {
    case red, yellow, green
}

let current = Light.red
switch current {
case .red:
    print("Stop")
case .yellow:
    print("Caution")
case .green:
    print("Go")
}

medium

A. No output

B. Go

C. Caution

D. Stop

Solution

1. Step 1: Identify the enum case assigned

   The variable current is assigned Light.red.

2. Step 2: Match the switch case for current

   The switch matches .red and prints "Stop".

3. Final Answer:

   Stop -> Option D

4. Quick Check:

   Light.red triggers "Stop" output [OK]

Hint: Match enum case in switch to get output [OK]

Common Mistakes:

• Confusing enum cases with strings
• Forgetting dot prefix in switch
• Assuming default output

4. Identify the error in this enum declaration:

enum Weather {
    case sunny
    case rainy
    case windy
    case
}

medium

A. Missing case name after 'case' keyword

B. Enum name is invalid

C. Curly braces are missing

D. Enum cases should be strings

Solution

1. Step 1: Review each enum case line

   The last line has case without a case name, which is invalid syntax.

2. Step 2: Confirm other parts are correct

   Enum name and braces are correct; cases do not need to be strings.

3. Final Answer:

   Missing case name after 'case' keyword -> Option A

4. Quick Check:

   Every 'case' must have a name [OK]

Hint: Each 'case' must have a name after it [OK]

Common Mistakes:

• Leaving 'case' empty
• Thinking cases need quotes
• Missing braces around enum

5. You want to create an enum Planet with cases for mercury, venus, and earth. Then, write a function that returns a friendly message for each planet. Which code correctly implements this?

hard

A. enum Planet { mercury, venus, earth }
func message(planet: Planet) -> String {
if planet == mercury { return "Closest to the Sun" }
else if planet == venus { return "Second planet" }
else { return "Our home" }
}

B. enum Planet { case mercury, venus, earth }
func message(for planet: Planet) -> String {
switch planet {
case .mercury: return "Closest to the Sun"
case .venus: return "Second planet"
case .earth: return "Our home"
}
}

C. enum Planet { case mercury, venus, earth }
func message(planet: Planet) -> String {
if planet == mercury { return "Closest to the Sun" }
else if planet == venus { return "Second planet" }
else { return "Our home" }
}

D. enum Planet { case mercury, venus, earth }
func message(for planet: Planet) -> String {
switch planet {
case mercury: return "Closest to the Sun"
case venus: return "Second planet"
case earth: return "Our home"
}
}

Solution

1. Step 1: Check enum declaration syntax

   Options A, C, and D declare enum correctly with case keyword; B misses it, so B is invalid.

2. Step 2: Check function parameter and switch usage

   enum Planet { case mercury, venus, earth } func message(for planet: Planet) -> String { switch planet { case .mercury: return "Closest to the Sun" case .venus: return "Second planet" case .earth: return "Our home" } } uses switch with dot syntax for cases and correct function signature. enum Planet { case mercury, venus, earth } func message(planet: Planet) -> String { if planet == mercury { return "Closest to the Sun" } else if planet == venus { return "Second planet" } else { return "Our home" } } uses if-else without dot syntax (.mercury), causing compile error. enum Planet { case mercury, venus, earth } func message(for planet: Planet) -> String { switch planet { case mercury: return "Closest to the Sun" case venus: return "Second planet" case earth: return "Our home" } } misses dot prefix in switch cases, causing error.

3. Final Answer:

   enum Planet { case mercury, venus, earth } func message(for planet: Planet) -> String { switch planet { case .mercury: return "Closest to the Sun" case .venus: return "Second planet" case .earth: return "Our home" } } -> Option B

4. Quick Check:

   Enum with 'case' and switch with dot cases [OK]

Hint: Use 'case' keyword and dot prefix in switch cases [OK]

Common Mistakes:

• Omitting 'case' keyword in enum
• Missing dot prefix in switch cases
• Using if without dot prefix for enum cases