Switch statement power in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a switch statement in Swift?

A switch statement lets you check a value against many possible cases. It helps you choose what code to run based on the value, like a traffic light deciding what color to show.

intermediate

How does Swift's switch differ from other languages?

Swift's switch is very powerful: it must be exhaustive (cover all cases), supports ranges, tuples, and where clauses for conditions, and does not need break statements to stop fall-through.

intermediate

What is the purpose of the where clause in a Swift switch case?

The where clause adds extra conditions to a case. It lets you check more than just the value, like saying 'match this case only if this extra rule is true'.

beginner

Explain how Swift switch handles multiple values in one case.

You can list multiple values separated by commas in one case. This means if the value matches any of them, that case runs. It's like saying 'if the value is this or that, do this'.

beginner

What happens if no case matches in a Swift switch statement?

Swift requires all possible values to be covered. If you don't cover all, you must add a default case to catch anything else. This keeps your code safe and predictable.

In Swift, what keyword is used to add extra conditions to a switch case?

A where

B if

C case

D else

The 'where' keyword lets you add extra conditions to a case in a switch statement.

Which of these is NOT true about Swift's switch statement?

A It can match tuples.

B It must cover all possible values.

C It supports matching ranges.

D It requires a break statement after each case.

Swift switch does NOT require break statements; it automatically stops after each case.

How do you handle values not matched by any case in Swift switch?

A Ignore them.

B Use a default case.

C Use an else statement.

D Use a catch block.

A default case catches any values not matched by other cases.

Can you list multiple values in one Swift switch case?

A No, only one value per case.

B Yes, but only with ranges.

C Yes, separated by commas.

D Only if they are strings.

You can list multiple values separated by commas in one case.

What does it mean that Swift switch is exhaustive?

A All possible values must be handled.

B It runs all cases every time.

C It only works with enums.

D It requires a default case always.

Exhaustive means all possible values must be covered by cases or a default.

Describe how Swift's switch statement can match complex patterns beyond simple values.

Think about how you can check more than just one value.

Explain why Swift requires switch statements to be exhaustive and how you can satisfy this requirement.

Consider what happens if a value doesn't match any case.

Practice

1. What is the main advantage of using a switch statement in Swift compared to multiple if-else statements?

easy

A. It runs faster than any other conditional statement.

B. It makes the code easier to read and maintain by clearly checking many cases.

C. It allows only numeric comparisons.

D. It automatically handles errors without extra code.

Solution

1. Step 1: Understand the purpose of switch

   The switch statement is designed to check a value against multiple cases clearly and cleanly.

2. Step 2: Compare with if-else statements

   While if-else can do similar checks, switch improves readability and maintenance by organizing cases neatly.

3. Final Answer:

   It makes the code easier to read and maintain by clearly checking many cases. -> Option B

4. Quick Check:

   Switch improves readability = A [OK]

Hint: Switch organizes multiple checks clearly for easy reading [OK]

Common Mistakes:

• Thinking switch is always faster than if-else
• Believing switch only works with numbers
• Assuming switch handles errors automatically

2. Which of the following is the correct syntax for a basic switch statement in Swift?

easy

A. switch (value) { case 1 print("One") else print("Other") }

B. switch value { if case 1: print("One") else: print("Other") }

C. switch value: case 1 -> print("One") else -> print("Other")

D. switch value { case 1: print("One") default: print("Other") }

Solution

1. Step 1: Review correct switch syntax

   In Swift, a switch statement uses curly braces with cases followed by colons and code blocks.

2. Step 2: Identify the correct option

   switch value { case 1: print("One") default: print("Other") } matches the correct syntax: switch value { case 1: ... default: ... }.

3. Final Answer:

   switch value { case 1: print("One") default: print("Other") } -> Option D

4. Quick Check:

   Correct switch syntax = B [OK]

Hint: Remember: cases end with colon and use curly braces [OK]

Common Mistakes:

• Omitting colons after case labels
• Using else instead of default
• Wrong punctuation like arrows or missing braces

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

let number = 3
switch number {
 case 1, 3, 5:
   print("Odd")
 case 2, 4, 6:
   print("Even")
 default:
   print("Unknown")
}

medium

A. Odd

B. Even

C. Unknown

D. No output

Solution

1. Step 1: Check the value of number

   The variable number is set to 3.

2. Step 2: Match number in switch cases

   Case 1, 3, 5 matches number 3, so it prints "Odd".

3. Final Answer:

   Odd -> Option A

4. Quick Check:

   3 in (1,3,5) = Odd [OK]

Hint: Look for matching case values separated by commas [OK]

Common Mistakes:

• Choosing Even because 3 is odd but not in even case
• Ignoring multiple values in one case
• Assuming default runs when a case matches

4. Identify the error in this Swift switch statement:

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

medium

A. Switch cannot use strings

B. Missing default case

C. Missing colon after case "B"

D. Print statements must be outside switch

Solution

1. Step 1: Check syntax of each case

   Each case label must end with a colon (:). The case "B" is missing this colon.

2. Step 2: Confirm other parts are correct

   Default case exists, strings are allowed, and print inside switch is valid.

3. Final Answer:

   Missing colon after case "B" -> Option C

4. Quick Check:

   Case labels need colon = C [OK]

Hint: Every case line ends with a colon : [OK]

Common Mistakes:

• Forgetting colon after case label
• Thinking default is optional (it is recommended)
• Believing switch can't handle strings

5. You want to categorize an integer score into grades using a switch statement:
- 90 to 100: "A"
- 80 to 89: "B"
- 70 to 79: "C"
- Below 70: "F"
Which switch statement correctly implements this?

hard

A. switch score {
case 90...100: print("A")
case 80...89: print("B")
case 70...79: print("C")
default: print("F")
}

B. switch score {
case 90..<100: print("A")
case 80..<90: print("B")
case 70..<80: print("C")
default: print("F")
}

C. switch score {
case 90...100: print("A")
case 80...90: print("B")
case 70...80: print("C")
default: print("F")
}

D. switch score {
case 90...100: print("A")
case 80...89: print("B")
case 70...79: print("C")
case 0...69: print("F")
}

Solution

1. Step 1: Understand range operators

   Closed range operator (...) includes both ends, so 90...100 includes 90 and 100.

2. Step 2: Check all ranges cover scores without overlap or gaps

   switch score { case 90...100: print("A") case 80...89: print("B") case 70...79: print("C") default: print("F") } uses closed ranges for exact matches (90-100, 80-89, 70-79) and default catches below 70 perfectly without gaps or overlaps.

3. Step 3: Identify issues in other options

   B uses half-open ranges (..<) excluding upper bounds like 100 (90..<100 misses 100); C has overlapping ranges (80...90 overlaps 90 with A, 70...80 overlaps 80); D lacks default and doesn't cover all integers (e.g., negatives, >100), causing compile error.

4. Final Answer:

   switch score { case 90...100: print("A") case 80...89: print("B") case 70...79: print("C") default: print("F") } -> Option A

5. Quick Check:

   Complete, non-overlapping ranges = A [OK]

Hint: Use closed ranges and cover all values explicitly [OK]

Common Mistakes:

• Overlapping or missing ranges
• Using half-open ranges that exclude max values
• Not covering all possible values explicitly