Switch with compound cases in Swift - Mini Project: Build & Apply

Switch with compound cases

📖 Scenario: Imagine you are building a simple app that categorizes fruits based on their names. You want to group some fruits together because they share similar characteristics.

🎯 Goal: You will create a program that uses a switch statement with compound cases to print the category of a fruit.

📋 What You'll Learn

Create a variable called fruit with the value "apple".

Create a variable called citrusFruits that holds the fruits "orange" and "lemon".

Use a switch statement on the fruit variable with compound cases to check if the fruit is an apple or banana, or if it is a citrus fruit.

Print the category of the fruit using print.

💡 Why This Matters

🌍 Real World

Grouping items by categories is common in apps that organize data, like grocery lists or inventory systems.

💼 Career

Understanding switch statements with compound cases helps in writing clear and efficient code for decision-making in many software projects.

1

Create the fruit variable

Create a variable called fruit and set it to the string "apple".

Swift

# Create a variable called fruit and set it to "apple"
# Your code here

Hint

Use var fruit = "apple" to create the variable.

2

Create the citrusFruits array

Create a variable called citrusFruits and set it to an array containing the strings "orange" and "lemon".

Swift

var fruit = "apple"
# Create a variable called citrusFruits with ["orange", "lemon"]
# Your code here

Hint

Use var citrusFruits = ["orange", "lemon"] to create the array.

3

Write the switch statement with compound cases

Write a switch statement on the variable fruit. Use compound cases to group "apple" and "banana" together, and use the citrusFruits array to group citrus fruits. For "apple" and "banana", print "Common fruit". For citrus fruits, print "Citrus fruit". For any other fruit, print "Other fruit".

Swift

var fruit = "apple"
var citrusFruits = ["orange", "lemon"]
# Write a switch statement on fruit with compound cases
# Your code here

Hint

Use case "apple", "banana" for the first group and case let x where citrusFruits.contains(x) for citrus fruits.

4

Print the result

Run the program to print the category of the fruit stored in fruit.

Swift

var fruit = "apple"
var citrusFruits = ["orange", "lemon"]
switch fruit {
case "apple", "banana":
    print("Common fruit")
case let x where citrusFruits.contains(x):
    print("Citrus fruit")
default:
    print("Other fruit")
}
# Run the program to see the output

Hint

The output should be Common fruit because fruit is "apple".

Practice

1.

What does a compound case in a Swift switch statement allow you to do?

easy

A. Skip the default case safely

B. Use multiple switch statements at once

C. Combine if and switch in one line

D. Match multiple values in a single case using commas

Solution

1. Step 1: Understand compound cases

   Compound cases let you list several values separated by commas in one case.

2. Step 2: Recognize the benefit

   This makes the code cleaner by avoiding repeated code for similar cases.

3. Final Answer:

   Match multiple values in a single case using commas -> Option D

4. Quick Check:

   Compound case = multiple values in one case [OK]

Hint: Look for commas inside a case to spot compound cases [OK]

Common Mistakes:

• Thinking compound cases combine multiple switches
• Believing compound cases skip default
• Confusing compound cases with if-else

2.

Which of the following is the correct syntax for a compound case in Swift?

switch value {
    case 1, 2, 3:
        print("One to three")
    default:
        print("Other")
}

easy

A. case 1, 2, 3:

B. case 1; 2; 3:

C. case (1, 2, 3):

D. case [1, 2, 3]:

Solution

1. Step 1: Recall Swift compound case syntax

   Swift uses commas to separate multiple values in one case.

2. Step 2: Check each option

   case 1, 2, 3: uses commas correctly; others use semicolons, parentheses, or brackets incorrectly.

3. Final Answer:

   case 1, 2, 3: -> Option A

4. Quick Check:

   Commas separate values in compound case [OK]

Hint: Use commas, not semicolons or brackets, for compound cases [OK]

Common Mistakes:

• Using semicolons instead of commas
• Putting values inside parentheses or brackets
• Missing the colon after case

3.

What will be printed by this Swift code?

let letter = "b"
switch letter {
case "a", "e", "i", "o", "u":
    print("Vowel")
case "b", "c", "d":
    print("Consonant")
default:
    print("Other")
}

medium

A. Vowel

B. No output

C. Consonant

D. Other

Solution

1. Step 1: Identify the value of letter

   The variable letter is "b".

2. Step 2: Match letter in switch cases

   "b" matches the second case with "b", "c", "d" which prints "Consonant".

3. Final Answer:

   Consonant -> Option C

4. Quick Check:

   "b" in second case = Consonant [OK]

Hint: Check which case list contains the value [OK]

Common Mistakes:

• Confusing vowels and consonants
• Forgetting to include default case
• Assuming no output if no exact match

4.

Find the error in this Swift switch statement:

let number = 3
switch number {
case 1, 2
    print("One or Two")
case 3:
    print("Three")
default:
    print("Other")
}

medium

A. Missing colon after case 1, 2

B. Missing default case

C. Cannot use compound cases with integers

D. Missing parentheses around 1, 2

Solution

1. Step 1: Check syntax of each case

   Each case must end with a colon (:). The first case is missing it.

2. Step 2: Verify other parts

   Default case is present; compound cases with integers are allowed; parentheses are not needed.

3. Final Answer:

   Missing colon after case 1, 2 -> Option A

4. Quick Check:

   Case lines must end with colon [OK]

Hint: Look for missing colons after case labels [OK]

Common Mistakes:

• Forgetting colon after case
• Thinking parentheses are required
• Believing compound cases disallow integers

5.

Given this Swift code, what will be the output?

let grade = "B"
switch grade {
case "A", "B", "C":
    print("Pass")
case "D", "F":
    print("Fail")
case "I", "W":
    print("Incomplete or Withdrawn")
default:
    print("Unknown grade")
}

hard

A. Incomplete or Withdrawn

B. Pass

C. Fail

D. Unknown grade

Solution

1. Step 1: Identify the value of grade

   The variable grade is "B".

2. Step 2: Match grade in compound cases

   "B" matches the first case "A", "B", "C" which prints "Pass".

3. Final Answer:

   Pass -> Option B

4. Quick Check:

   "B" in first case = Pass [OK]

Hint: Match value to any in compound case list [OK]

Common Mistakes:

• Assuming "B" is a fail grade
• Ignoring default case
• Confusing case groups