No implicit fallthrough in switch in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to match the number to its English word using a switch statement.

Swift

let number = 2
var word = ""
switch number {
case 1:
    word = "One"
case 2:
    word = [1]
default:
    word = "Unknown"
}
print(word)

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

A"Two"

B"2"

C2

D"Second"

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning a number instead of a string.

Forgetting the quotes around the word.

The case for number 2 should assign the string "Two" to the variable word.

2fill in blank

medium

Complete the switch statement to print the correct message for the grade.

Swift

let grade = "B"
switch grade {
case "A":
    print("Excellent")
case [1]:
    print("Good")
default:
    print("Needs Improvement")
}

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

A"C"

B"D"

C"B"

D"F"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a character without quotes.

Using the wrong grade letter.

The case should match the grade "B" to print "Good".

3fill in blank

hard

Fix the error in the switch statement by completing the missing case value.

Swift

let day = 3
switch day {
case 1:
    print("Monday")
case [1]:
    print("Tuesday")
default:
    print("Other day")
}

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

A2

B"2"

C3

D"3"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string instead of an integer for the case.

Using the wrong number for the case.

The case should be 2 without quotes because day is an integer.

4fill in blank

hard

Fill both blanks to create a switch that prints the correct season for the month number.

Swift

let month = 4
switch month {
case [1]:
    print("Winter")
case [2]:
    print("Spring")
default:
    print("Other season")
}

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

A12

B3

C4

D6

Attempts:

3 left

💡 Hint

Common Mistakes

Using string values instead of integers.

Mixing up the month numbers for seasons.

Month 12 is winter, and month 4 is spring.

5fill in blank

hard

Fill all three blanks to create a switch that prints the day type based on the day number.

Swift

let dayNumber = 6
switch dayNumber {
case [1]:
    print("Weekday")
case [2]:
    print("Weekend")
case [3]:
    print("Weekend")
default:
    print("Invalid day")
}

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

A1

B6

C7

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning weekend to wrong day numbers.

Using strings instead of integers.

Days 1 to 5 are weekdays, 6 and 7 are weekends.

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