Labeled break and continue in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a labeled break in Kotlin?

A labeled break in Kotlin is a way to exit a specific loop when you have nested loops. You put a label before the loop and use break with that label to stop that loop.

beginner

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

You define a label by writing a name followed by the @ symbol before the loop. For example: outer@ for (i in 1..5) { ... }.

intermediate

What does a labeled continue do in Kotlin?

A labeled continue skips the current iteration of the labeled loop and moves to the next iteration of that loop, even if it is an outer loop.

intermediate

Why use labeled break or continue instead of regular break or continue?

Regular break or continue only affect the innermost loop. Labeled versions let you control outer loops directly, which is useful when you have nested loops and want to jump out or skip iterations in outer loops.

intermediate

Example: What will this Kotlin code print?

outer@ for (i in 1..3) {
  for (j in 1..3) {
    if (i == 2 && j == 2) break@outer
    print("($i,$j) ")
  }
}

It will print: (1,1) (1,2) (1,3) (2,1) Because when i=2 and j=2, the labeled break exits the outer loop before printing (2,2).

What does the label in Kotlin loops look like?

A A name followed by @ before the loop

B A name followed by # before the loop

C A name inside parentheses after the loop

D A name after the loop with a colon

Labels are defined by writing a name followed by @ before the loop, like label@ for (...) { ... }.

What happens when you use break@label inside nested loops?

A It breaks only the innermost loop

B It causes a syntax error

C It continues the innermost loop

D It breaks out of the loop with the given label

break@label exits the loop that has the matching label.

Which statement is true about labeled continue in Kotlin?

A It restarts the program

B It breaks out of the labeled loop

C It skips to the next iteration of the labeled loop

D It only works with single loops

Labeled continue skips the current iteration of the labeled loop and moves to its next iteration.

Why might you use a labeled break instead of a regular break?

A To exit an outer loop from inside an inner loop

B To exit only the innermost loop

C To skip the rest of the current iteration

D To pause the loop

Labeled break lets you exit an outer loop directly from inside nested loops.

What will happen if you use a label that does not exist with break or continue?

A It breaks the innermost loop

B Compilation error

C It continues the innermost loop

D It ignores the label and runs normally

Using a non-existent label causes a compilation error in Kotlin.

Explain how labeled break works in Kotlin and give a simple example.

Think about how to stop an outer loop from inside an inner loop.

Describe the difference between regular continue and labeled continue in Kotlin.

Consider what happens when you want to skip iterations in outer loops.

Practice

1. What does the break@label statement do in Kotlin nested loops?

easy

A. It stops the loop identified by the label immediately.

B. It skips the current iteration of the innermost loop.

C. It restarts the entire program from the beginning.

D. It pauses the loop until a condition is met.

Solution

1. Step 1: Understand labeled break usage

   The break@label statement is used to exit a specific loop marked by the label, not just the innermost loop.

2. Step 2: Compare with other options

   Options B and D describe continue or pause behavior, which is incorrect. It restarts the entire program from the beginning. is unrelated to loop control.

3. Final Answer:

   It stops the loop identified by the label immediately. -> Option A

4. Quick Check:

   break@label stops labeled loop [OK]

Hint: break@label exits the labeled loop immediately [OK]

Common Mistakes:

• Confusing break@label with continue@label
• Thinking break@label only stops innermost loop
• Assuming break@label pauses instead of stops

2. Which of the following is the correct syntax to continue the outer loop labeled outerLoop in Kotlin?

easy

A. continue#outerLoop

B. continue outerLoop

C. continue(outerLoop)

D. continue@outerLoop

Solution

1. Step 1: Recall Kotlin labeled continue syntax

   Kotlin uses the @ symbol to refer to labels with break or continue, so the correct syntax is continue@label.

2. Step 2: Eliminate incorrect options

   Options B, C, and D use invalid syntax for labels in Kotlin.

3. Final Answer:

   continue@outerLoop -> Option D

4. Quick Check:

   Use continue@label to continue labeled loop [OK]

Hint: Use @ symbol with label for continue or break [OK]

Common Mistakes:

• Omitting @ symbol before label
• Using parentheses or other symbols with label
• Confusing syntax with other languages

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

outer@ for (i in 1..3) {
    inner@ for (j in 1..3) {
        if (i == 2 && j == 2) break@outer
        print("$i$j ")
    }
}

medium

A. 11 12 13 21 22

B. 11 12 13 21

C. 11 12 13 21 22 23

D. 11 12 13

Solution

1. Step 1: Trace nested loops and break condition

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

2. Step 2: List printed values before break

   For i=1, j=1..3 prints 11 12 13. For i=2, j=1 prints 21, then at j=2 break@outer stops all loops. So output is "11 12 13 21".

3. Final Answer:

   11 12 13 21 -> Option B

4. Quick Check:

   break@outer stops all loops at i=2,j=2 [OK]

Hint: break@label stops all loops at labeled point [OK]

Common Mistakes:

• Assuming break@outer only stops inner loop
• Including values after break condition
• Confusing break@outer with continue@outer

4. Identify the error in this Kotlin code snippet:

outer@ for (i in 1..2) {
    for (j in 1..2) {
        if (i == 1) continue outer
        println("i=$i, j=$j")
    }
}

medium

A. continue@outer should be used instead of continue outer.

B. continue cannot be used with a label on an inner loop.

C. Label 'outer' is not defined.

D. No error; code runs correctly.

Solution

1. Step 1: Check labeled continue syntax

   Kotlin requires the @ symbol when using labels with break or continue, so it must be continue@outer.

2. Step 2: Verify label definition and usage

   The label 'outer' is correctly defined, so Label 'outer' is not defined. is wrong. Using continue with label without @ causes syntax error.

3. Final Answer:

   continue@outer should be used instead of continue outer. -> Option A

4. Quick Check:

   Use continue@label syntax to avoid errors [OK]

Hint: Always use @ with label in continue or break [OK]

Common Mistakes:

• Omitting @ symbol in labeled continue
• Thinking label must be on inner loop
• Assuming no error when syntax is wrong

5. Given nested loops labeled outer and inner, how can you skip only the current iteration of the outer loop when a condition in the inner loop is met?

hard

A. Use break@outer inside inner loop.

B. Use continue without label inside inner loop.

C. Use continue@outer inside inner loop.

D. Use break without label inside inner loop.

Solution

1. Step 1: Understand labeled continue effect

   Using continue@outer skips the current iteration of the outer loop, moving to the next iteration of outer.

2. Step 2: Compare with break and unlabeled continue

   break@outer would exit the outer loop entirely, not just skip iteration. Unlabeled continue affects only inner loop.

3. Final Answer:

   Use continue@outer inside inner loop. -> Option C

4. Quick Check:

   continue@outer skips outer loop iteration [OK]

Hint: Use continue@label to skip labeled loop iteration [OK]

Common Mistakes:

• Using break@outer instead of continue@outer
• Using unlabeled continue to skip outer loop
• Confusing break and continue effects