No implicit fallthrough in switch in Swift - Mini Project: Build & Apply

No Implicit Fallthrough in Switch

📖 Scenario: Imagine you are creating a simple program that tells the type of a fruit based on its name. You will use a switch statement to check the fruit name and print a message. Swift's switch statements do not allow implicit fallthrough, so each case must be handled explicitly.

🎯 Goal: Build a Swift program that uses a switch statement without implicit fallthrough to print the type of fruit based on a given fruit name.

📋 What You'll Learn

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

Create a variable called fruitType and set it to an empty string.

Use a switch statement on fruit with cases for "Apple", "Banana", and "Orange".

Assign fruitType a string describing the fruit type inside each case.

Print the fruitType variable.

💡 Why This Matters

🌍 Real World

Switch statements are used in many apps to handle different options or commands clearly and safely without accidental code running.

💼 Career

Understanding Swift's switch behavior is important for iOS app developers to write clear and bug-free decision-making code.

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 fruitType variable

Create a variable called fruitType and set it to an empty string "".

Swift

var fruit = "Apple"
# Create a variable called fruitType and set it to an empty string
# Your code here

Hint

Use var fruitType = "" to create the variable.

3

Use switch to assign fruitType

Use a switch statement on the variable fruit. Add cases for "Apple", "Banana", and "Orange". Inside each case, assign fruitType a string describing the fruit type: "Apple is a pome fruit", "Banana is a berry", and "Orange is a citrus fruit" respectively. Remember, Swift does not allow implicit fallthrough, so do not add fallthrough.

Swift

var fruit = "Apple"
var fruitType = ""
# Use switch on fruit to assign fruitType for "Apple", "Banana", and "Orange"
# Your code here

Hint

Use switch fruit { case "Apple": ... } and assign fruitType inside each case. Do not use fallthrough.

4

Print the fruitType

Write a print statement to display the value of the variable fruitType.

Swift

var fruit = "Apple"
var fruitType = ""
switch fruit {
case "Apple":
    fruitType = "Apple is a pome fruit"
case "Banana":
    fruitType = "Banana is a berry"
case "Orange":
    fruitType = "Orange is a citrus fruit"
default:
    fruitType = "Unknown fruit type"
}
# Print the fruitType variable
# Your code here

Hint

Use print(fruitType) to show the result.

Practice

1. What happens if you do not use fallthrough in a Swift switch statement?

easy

A. Only the matched case runs; no automatic fallthrough to the next case.

B. All cases after the matched one run automatically.

C. The program throws a runtime error.

D. The switch statement ignores the matched case.

Solution

1. Step 1: Understand Swift switch behavior

   Swift switch statements do not automatically continue to the next case after a match.

2. Step 2: Role of fallthrough keyword

   To continue to the next case, you must explicitly use the fallthrough keyword.

3. Final Answer:

   Only the matched case runs; no automatic fallthrough to the next case. -> Option A

4. Quick Check:

   No implicit fallthrough = matched case only [OK]

Hint: Remember: Swift switch stops after matched case unless fallthrough used [OK]

Common Mistakes:

• Assuming all cases run after a match like in C
• Forgetting to add fallthrough when needed
• Expecting runtime errors without fallthrough
• Thinking switch ignores matched cases

2. Which of the following is the correct syntax to explicitly continue to the next case in a Swift switch?

easy

A. Use the keyword continue inside the case.

B. No syntax needed; Swift does it automatically.

C. Use the keyword fallthrough inside the case.

D. Use a comma , between cases.

Solution

1. Step 1: Identify the keyword for fallthrough

   Swift uses the keyword fallthrough to continue to the next case.

2. Step 2: Eliminate incorrect options

   continue is for loops, commas separate cases but don't cause fallthrough, and Swift does not do it automatically.

3. Final Answer:

   Use the keyword fallthrough inside the case. -> Option C

4. Quick Check:

   Explicit fallthrough keyword = fallthrough [OK]

Hint: Use fallthrough keyword to continue to next case in Swift switch [OK]

Common Mistakes:

• Confusing fallthrough with continue
• Using commas to join cases expecting fallthrough
• Assuming automatic fallthrough without keyword
• Using break to continue to next case

3. What is the output of the following Swift code?

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

medium

A. Three

B. Two
Three

C. Two

D. Two
Three
Other

Solution

1. Step 1: Identify matched case

   The value 2 matches case 2, so it prints "Two".

2. Step 2: Check for fallthrough

   Since fallthrough is used, execution continues to case 3, printing "Three".

3. Final Answer:

   Two Three -> Option B

4. Quick Check:

   fallthrough causes next case to run = Two and Three [OK]

Hint: Look for fallthrough keyword to know if next case runs [OK]

Common Mistakes:

• Ignoring fallthrough and printing only "Two"
• Printing "Three" only without "Two"
• Expecting default case to run
• Assuming all cases print

4. Identify the error in this Swift switch statement:

let value = 3
switch value {
 case 1:
   print("One")
 case 2:
   print("Two")
 case 3:
   print("Three")
   fallthrough
 case 4:
   print("Four")
   fallthrough
 case 5:
   print("Five")
}

medium

A. Missing default case causes a compile error.

B. Multiple fallthroughs cause a runtime error.

C. No error; code runs and prints Three, Four, Five.

D. Fallthrough cannot be used in the last case.

Solution

1. Step 1: Exhaustiveness requirement

   Swift switch on Int must be exhaustive: cover all possible values or add default. Cases 1-5 don't cover all Ints, no default: compile error.

2. Step 2: Fallthrough usage is valid

   Fallthroughs in cases 3 and 4 are allowed; no fallthrough in case 5 (correct); multiples OK, no runtime issues.

3. Final Answer:

   Missing default case causes a compile error. -> Option A

4. Quick Check:

   Non-exhaustive switch on Int = compile error [OK]

Hint: Swift switch on Int needs default unless all cases covered [OK]

Common Mistakes:

• Picking A: no fallthrough in last case
• Picking B: multiple fallthroughs allowed
• Picking C: ignores compile-time exhaustiveness error
• Thinking value=3 makes it exhaustive

5. You want to print all numbers from a matched case up to 5 in a Swift switch. Which code correctly uses fallthrough to achieve this?

let num = 3
switch num {
 case 1:
   print(1)
   fallthrough
 case 2:
   print(2)
   fallthrough
 case 3:
   print(3)
   fallthrough
 case 4:
   print(4)
   fallthrough
 case 5:
   print(5)
 default:
   print("Done")
}

hard

A. This code prints 1 to 5 regardless of num.

B. This code prints only 3 when num is 3.

C. This code causes a compile error due to fallthrough in default.

D. This code prints 3, 4, 5 when num is 3.

Solution

1. Step 1: Identify matched case and fallthrough chain

   When num is 3, case 3 matches and prints 3, then fallthrough continues to cases 4 and 5 printing 4 and 5.

2. Step 2: Confirm output and default usage

   Default is not reached because cases 3 to 5 cover the fallthrough chain; no error occurs.

3. Final Answer:

   This code prints 3, 4, 5 when num is 3. -> Option D

4. Quick Check:

   Fallthrough chains print from matched case to end [OK]

Hint: Use fallthrough in each case to print all following cases [OK]

Common Mistakes:

• Expecting only matched case to print
• Thinking default runs after fallthrough chain
• Assuming compile error from fallthrough in default
• Believing all cases print regardless of match