Breaking out of loops and avoiding infinite loops

Overview

How a flag-controlled search loop works, infinite loop and loop guard.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What does break do inside a loop?

   Model answer

   A break abandons the loop immediately, so no further passes occur and execution continues at the first statement after the loop.

2. 2

   What does continue do inside a loop?

   Model answer

   A continue abandons the rest of the current pass only, so execution jumps to the loop update and condition and the loop carries on.

3. 3

   for (int i = 1; i <= 5; i++) { if (i == 3) { break; } System.out.print(i + " "); } — what does this fragment print?

   Model answer

   The loop prints 1 and then 2, and on the third pass the break leaves the loop before the printing statement, so the output is 1 2.

4. 4

   for (int i = 1; i <= 5; i++) { if (i == 3) { continue; } System.out.print(i + " "); } — what does this fragment print?

   Model answer

   Only the pass with the counter at 3 is cut short, and the remaining passes print as normal, so the output is 1 2 4 5.

5. 5

   Why do some programmers avoid break, and what is the structured alternative?

   Model answer

   A break gives the loop a second exit point, which makes the flow harder to follow; the structured alternative is a boolean flag set inside the loop and tested in the loop condition.

6. 6

   Describe how a flag-controlled search loop works.

   Model answer

   A boolean flag starts false and the loop continues while the flag is false and items remain; when the wanted item is met the flag is set to true, which ends the loop at the next test without a break.

Other ways to work this

The same content, four other ways.

What is inside Levo

Six ways to work the same material.