Labelled break and continue in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a labelled break in Go?

A labelled break in Go is used to exit an outer loop from inside an inner loop by specifying the label name of the outer loop.

beginner

How does labelled continue differ from a normal continue in Go?

Labelled continue skips the current iteration of the loop identified by the label, which can be an outer loop, while normal continue only affects the innermost loop.

beginner

Show the syntax of a labelled break in Go.

labelName: for condition { for condition { if someCondition { break labelName } } }

intermediate

Why use labelled break or continue instead of normal break or continue?

They allow you to control outer loops directly from inner loops, making it easier to manage complex nested loops without extra flags or complicated logic.

beginner

Can you use labelled break or continue without defining a label?

No, labelled break and continue require a label to specify which loop to affect. Without a label, break and continue only affect the innermost loop.

What does a labelled break do in Go?

A Exits the loop with the specified label

B Skips the current iteration of the innermost loop

C Restarts the program

D Pauses the loop execution

A labelled break exits the loop identified by the label, which can be an outer loop.

Which keyword is used to skip to the next iteration of a labelled loop in Go?

A next

B break

C skip

D continue

The continue keyword, when used with a label, skips to the next iteration of the labelled loop.

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

A It breaks the outermost loop

B It breaks the innermost loop only

C It breaks all loops

D It causes a compile error

A break without a label only exits the innermost loop.

Is this valid Go code? outer: for i := 0; i < 3; i++ { for j := 0; j < 3; j++ { if j == 1 { continue outer } } }

A Yes, but it breaks the outer loop

B No, continue cannot have a label

C Yes, it continues the outer loop

D No, labels cannot be used with continue

In Go, continue can be used with a label to skip to the next iteration of the labelled loop.

What is the purpose of labels in Go loops?

A To name loops for use with break and continue

B To declare variables

C To define functions

D To comment code

Labels name loops so break and continue can refer to outer loops.

Explain how labelled break works in Go with an example.

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

Describe the difference between normal continue and labelled continue in Go.

Consider which loop each continue affects.

Practice

1. What is the main purpose of using a labelled break in Go nested loops?

easy

A. To declare a new variable inside the loop

B. To exit from an outer loop directly

C. To restart the entire program

D. To skip the current iteration of the inner loop

Solution

1. Step 1: Understand labelled break usage

   A labelled break lets you exit a specific loop, usually an outer one, directly from inside nested loops.

2. Step 2: Compare with normal break

   Normal break exits only the innermost loop, but labelled break can exit outer loops by specifying the label.

3. Final Answer:

   To exit from an outer loop directly -> Option B

4. Quick Check:

   Labelled break = exit outer loop [OK]

Hint: Labelled break jumps out of outer loops directly [OK]

Common Mistakes:

• Thinking break skips iteration instead of exiting loop
• Confusing labelled break with continue
• Assuming break restarts loops

2. Which of the following is the correct syntax to use a labelled continue in Go?

easy

A. continue labelName

B. continue to labelName

C. continue(labelName)

D. continue; labelName

Solution

1. Step 1: Recall labelled continue syntax

   In Go, to continue a labelled loop, you write continue labelName without parentheses or extra keywords.

2. Step 2: Check other options

   Options A, B, and D use incorrect syntax like extra words, parentheses, or semicolons which are invalid in Go.

3. Final Answer:

   continue labelName -> Option A

4. Quick Check:

   Labelled continue syntax = continue labelName [OK]

Hint: Use 'continue' followed by label name without punctuation [OK]

Common Mistakes:

• Adding parentheses around label
• Using extra words like 'to' or semicolons
• Confusing break and continue syntax

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

outer:
for i := 1; i <= 3; i++ {
    for j := 1; j <= 3; j++ {
        if i*j > 3 {
            break outer
        }
        fmt.Print(i*j, " ")
    }
}

medium

A. 1 2 3 2

B. 1 2 3 2 4 6 3 6 9

C. 1 2 2 3

D. 1 2 2 3 3

Solution

1. Step 1: Trace the nested loops and condition

   For i=1, j=1 to 3: i*j = 1,2,3 (all ≤ 3), so prints "1 2 3 ". For i=2, j=1: i*j=2 (≤3), prints "2 ". Next j=2: i*j=4 (>3), triggers break outer which exits the outer loop immediately.

2. Step 2: Understand break outer effect

   Since break outer exits both loops, no further printing occurs after i=2, j=2 check.

3. Final Answer:

   1 2 3 2 -> Option A

4. Quick Check:

   Labelled break exits outer loop at i*j>3 [OK]

Hint: Labelled break exits all loops at condition [OK]

Common Mistakes:

• Ignoring labelled break effect and continuing loops
• Confusing break with continue
• Miscomputing i*j values

4. Identify the error in this Go code snippet using labelled continue:

outer:
for i := 0; i < 3; i++ {
    for j := 0; j < 3; j++ {
        if i == j {
            continue
        }
        fmt.Println(i, j)
    }
}

medium

A. continue cannot be used inside nested loops

B. Label 'outer' is not defined before the loops

C. Missing label after continue to specify which loop to continue

D. fmt.Println syntax is incorrect

Solution

1. Step 1: Check labelled continue usage

   The code defines label 'outer' but uses plain continue inside inner loop. To continue the outer loop, it must be continue outer.

2. Step 2: Understand effect of missing label

   Without label, continue only skips current inner loop iteration, not the outer loop. The label is unused, which is likely a mistake.

3. Final Answer:

   Missing label after continue to specify which loop to continue -> Option C

4. Quick Check:

   Labelled continue needs label after continue [OK]

Hint: Use label after continue to affect outer loops [OK]

Common Mistakes:

• Using continue without label when label is defined
• Assuming continue skips outer loop without label
• Confusing label placement

5. Given nested loops labelled outer and inner, how would you skip the rest of the current iteration of the outer loop from inside the inner loop in Go?

hard

A. Use break inner inside the inner loop

B. Use break outer inside the outer loop

C. Use continue inner inside the outer loop

D. Use continue outer inside the inner loop

Solution

1. Step 1: Understand labelled continue behavior

   Using continue outer inside the inner loop skips the rest of the current iteration of the outer loop and moves to the next iteration of the outer loop.

2. Step 2: Differentiate from break and other options

   break inner exits the inner loop, but does not skip outer loop iteration. continue inner affects inner loop only. break outer exits the outer loop entirely.

3. Final Answer:

   Use continue outer inside the inner loop -> Option D

4. Quick Check:

   Labelled continue skips outer loop iteration [OK]

Hint: Use 'continue' with outer label to skip outer iteration [OK]

Common Mistakes:

• Using break instead of continue to skip iteration
• Applying continue to wrong loop label
• Confusing break and continue effects