Switch statement power in Swift - Step-by-Step Execution

Concept Flow - Switch statement power

Start with a value

↓

Evaluate switch expression

↓

Check case 1

No→Check case 2

↓

Execute case 1

↓

Exit switch

The switch statement checks a value against multiple cases and runs the matching case's code, or the default if none match.

Execution Sample

Swift

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

This code checks the number and prints a message depending on its value.

Execution Table

Step	Switch Expression	Case Checked	Match?	Action	Output
1	3	case 1	No	Skip
2	3	case 2, 3	Yes	Execute print	Two or Three
3	3	default	Skipped	Exit switch

💡 Matched case 2, 3; executed print and exited switch

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
number	3	3	3	3

Key Moments - 2 Insights

Why does the switch stop after matching case 2, 3 and not check default?

In Swift, once a case matches and executes, the switch exits automatically (see execution_table step 3). No fall-through happens unless explicitly stated.

Can a case check multiple values like case 2, 3?

Yes, Swift allows multiple values in one case separated by commas, so case 2, 3 matches if the value is 2 or 3 (see execution_table step 2).

Visual Quiz - 3 Questions

Look at the execution table, what is the output at step 2?

A "Two or Three"

B "One"

C "Other"

D No output

💡 Hint

Check the 'Output' column at step 2 in the execution_table.

At which step does the switch statement stop checking cases?

A Step 1

B Step 2

C Step 3

D It checks all cases

💡 Hint

Look at the 'Match?' and 'Action' columns in execution_table to see when it stops.

If number was 5, what would be the output?

A "One"

B "Two or Three"

C "Other"

D No output

💡 Hint

Refer to the default case in the code and execution_table logic.

Concept Snapshot

switch value {
 case val1:
   // code
 case val2, val3:
   // code
 default:
   // code
}
- Checks value against cases
- Runs matching case code
- Exits after first match
- Default runs if no match

Full Transcript

This visual execution shows how a Swift switch statement works. It starts by evaluating the value to check. Then it compares this value to each case in order. If a case matches, it runs that case's code and stops checking further cases. If no case matches, it runs the default case. In the example, the number 3 matches the case with 2 and 3, so it prints "Two or Three" and exits. Variables remain unchanged during this process. This helps beginners see exactly how switch chooses which code to run.

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