Conditional repetition with WHILE and DO WHILE

Overview

Conditional repetition and sentinel value.

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 is conditional repetition?

   Model answer

   Conditional repetition repeats a block for as long as a condition remains true, so the number of passes depends on the data and is not known before the loop starts.

2. 2

   How does a pre-test loop differ from a post-test loop?

   Model answer

   A pre-test loop evaluates its condition before the body, so the body may never run at all, while a post-test loop evaluates the condition after the body, so the body always runs at least once.

3. 3

   Give the general form of a while loop in Java.

   Model answer

   The general form is while (condition) { statements }, with the condition tested before each pass and the loop ending as soon as the condition is false.

4. 4

   How many times does the body of a while loop execute when the condition is false at the outset?

   Model answer

   The body executes no times at all, because a while loop tests its condition before the first pass.

5. 5

   How many times does the body of a do while loop execute at minimum, and why?

   Model answer

   The body executes at least once, because the condition of a do while loop is not tested until the body has already run.

6. 6

   int n = 5; while (n > 0) { System.out.print(n + " "); n = n - 2; } — what does this fragment print?

   Model answer

   The loop prints 5, then 3, then 1, and the next subtraction leaves n at −1, which fails the condition, so the output is 5 3 1.

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