Labeled statements for nested loops in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a labeled statement in Swift?

A labeled statement is a name given to a loop or block of code, allowing you to control flow explicitly, especially useful for nested loops.

beginner

How do you define a label for a loop in Swift?

You write the label name followed by a colon before the loop. For example:
outerLoop: for i in 1...3 { ... }

intermediate

Why use labeled statements with nested loops?

They let you break or continue an outer loop directly from inside an inner loop, making it easier to control complex loop flows.

beginner

What happens if you use 'break' without a label inside nested loops?

The 'break' will only exit the innermost loop, not the outer loops.

intermediate

Example: How to break out of an outer loop named 'outerLoop' from inside an inner loop?

Use break outerLoop inside the inner loop to exit the outer loop immediately.

How do you label a loop named 'mainLoop' in Swift?

A mainLoop: for i in 1...5 { }

B for mainLoop in 1...5 { }

C label mainLoop for i in 1...5 { }

D for i in 1...5 mainLoop: { }

The correct syntax is to write the label followed by a colon before the loop.

What does 'break outerLoop' do inside nested loops?

A Continues the outer loop

B Exits only the innermost loop

C Exits the loop labeled 'outerLoop'

D Causes a syntax error

'break outerLoop' exits the loop that has the label 'outerLoop'.

If you want to skip the current iteration of an outer loop from inside an inner loop, what do you use?

A continue outerLoop

B skip outerLoop

C break outerLoop

D continue

'continue outerLoop' skips the current iteration of the loop labeled 'outerLoop'.

What happens if you use 'break' without a label inside nested loops?

A Breaks all loops

B Breaks only the innermost loop

C Breaks the outermost loop

D Does nothing

'break' without a label exits only the innermost loop.

Which of these is a valid use of a labeled statement in Swift?

A while true { break outer }

B label outer while true { break }

C while true outer: { break }

D outer: while true { break outer }

Label must be before the loop, and 'break outer' correctly exits the labeled loop.

Explain how labeled statements help control flow in nested loops in Swift.

Think about how you can exit or skip outer loops from inside inner loops.

Write a simple Swift code example using a labeled statement to break out of an outer loop from inside an inner loop.

Use a label before the outer loop and 'break labelName' inside the inner loop.

Practice

1. What is the main purpose of using labeled statements in nested loops in Swift?

easy

A. To speed up the loop execution

B. To declare variables inside loops

C. To directly control which loop to break or continue

D. To automatically optimize memory usage

Solution

1. Step 1: Understand labeled statements

   Labeled statements give a name to loops so you can refer to them directly.

2. Step 2: Control flow in nested loops

   This naming allows breaking or continuing an outer loop from inside an inner loop without extra flags.

3. Final Answer:

   To directly control which loop to break or continue -> Option C

4. Quick Check:

   Labeled loops control flow directly = C [OK]

Hint: Labels let you break/continue outer loops easily [OK]

Common Mistakes:

• Thinking labels declare variables
• Assuming labels improve speed
• Confusing labels with memory optimization

2. Which of the following is the correct syntax to label a loop named 'outerLoop' in Swift?

easy

A. for outerLoop in 1...3 { }

B. outerLoop: for i in 1...3 { }

C. for i in 1...3 outerLoop: { }

D. label outerLoop for i in 1...3 { }

Solution

1. Step 1: Recall label syntax in Swift

   Labels are written as a name followed by a colon before the loop statement.

2. Step 2: Match syntax to options

   outerLoop: for i in 1...3 { } correctly places 'outerLoop:' before the for loop.

3. Final Answer:

   outerLoop: for i in 1...3 { } -> Option B

4. Quick Check:

   Label name + colon before loop = A [OK]

Hint: Label name ends with colon before loop starts [OK]

Common Mistakes:

• Placing label after the loop
• Using 'label' keyword (not valid)
• Putting label inside loop braces

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

outerLoop: for i in 1...2 {
    for j in 1...3 {
        if j == 2 {
            break outerLoop
        }
        print("\(i),\(j)")
    }
}

medium

A. 1,1
1,2
1,3
2,1
2,2
2,3

B. 1,1
1,2

C. 1,1
2,1

D. 1,1

Solution

1. Step 1: Understand loop and break behavior

   The outer loop runs i from 1 to 2, inner loop j from 1 to 3. When j == 2, break outerLoop stops the outer loop entirely.

2. Step 2: Trace iterations

   First iteration: i=1, j=1 prints "1,1". When j=2, break outerLoop triggers, stopping all loops immediately.

3. Final Answer:

   1,1 -> Option D

4. Quick Check:

   Break outer loop at j=2 stops all = D [OK]

Hint: Break with label stops outer loop immediately [OK]

Common Mistakes:

• Thinking break only stops inner loop
• Expecting all prints before break
• Ignoring label effect on break

4. Identify the error in this Swift code using labeled statements:

outer: for i in 1...2 {
    for j in 1...2 {
        if j == 2 {
            break outerLoop
        }
        print(i, j)
    }
}

medium

A. Label 'outerLoop' is not defined

B. Syntax error: missing colon after label

C. Cannot use break inside nested loops

D. No error, code runs fine

Solution

1. Step 1: Check label definition

   The loop is labeled 'outer', but break tries to use 'outerLoop' which is undefined.

2. Step 2: Understand label usage

   Labels must match exactly. Using a different name causes a compile error.

3. Final Answer:

   Label 'outerLoop' is not defined -> Option A

4. Quick Check:

   Break label must match defined label = B [OK]

Hint: Break label must exactly match loop label name [OK]

Common Mistakes:

• Using different label names
• Forgetting colon after label
• Thinking break can't be used in nested loops

5. Given the task to print all pairs (i, j) where i and j range from 1 to 3, but stop all loops immediately when i + j equals 4, which Swift code correctly uses labeled statements to achieve this?

hard

A. outerLoop: for i in 1...3 {
for j in 1...3 {
if i + j == 4 {
break outerLoop
}
print("\(i),\(j)")
}
}

B. for i in 1...3 {
for j in 1...3 {
if i + j == 4 {
break
}
print(i, j)
}
}

C. outerLoop: for i in 1...3 {
for j in 1...3 {
if i + j == 4 {
continue outerLoop
}
print(i, j)
}
}

D. for i in 1...3 {
for j in 1...3 {
if i + j == 4 {
continue
}
print(i, j)
}
}

Solution

1. Step 1: Understand the stopping condition

   We want to stop all loops immediately when i + j == 4, so we must break the outer loop.

2. Step 2: Use labeled break correctly

   outerLoop: for i in 1...3 { for j in 1...3 { if i + j == 4 { break outerLoop } print("\(i),\(j)") } } uses 'break outerLoop' to stop the outer loop from inside the inner loop, which is correct.

3. Step 3: Check other options

   for i in 1...3 { for j in 1...3 { if i + j == 4 { break } print(i, j) } } breaks only inner loop; C uses continue which skips iterations but doesn't stop loops; D continues inner loop only.

4. Final Answer:

   Code that breaks outerLoop when i + j == 4 -> Option A

5. Quick Check:

   Labeled break stops all loops = A [OK]

Hint: Use labeled break to stop outer loop from inner loop [OK]

Common Mistakes:

• Using break without label stops only inner loop
• Using continue instead of break
• Not labeling the outer loop