Counter-based while loop in Java - Cheat Sheet & Quick Revision

Recall & Review

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What is a counter-based while loop?

A counter-based while loop repeats a block of code while a counter variable meets a condition, usually increasing or decreasing the counter each time to eventually stop the loop.

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Why do we need a counter variable in a while loop?

The counter variable helps control how many times the loop runs. It changes each time the loop runs so the loop can stop when the counter reaches a limit.

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What happens if the counter is not updated inside a while loop?

If the counter is not updated, the loop condition may never become false, causing an infinite loop that runs forever.

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Example: What does this code print? int i = 1; while (i <= 3) { System.out.println(i); i++; }

It prints: 1 2 3 The loop starts with i=1 and prints i, then increases i by 1 each time until i is greater than 3.

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How to avoid infinite loops in counter-based while loops?

Always update the counter inside the loop so the condition will eventually become false. Also, check the loop condition carefully before running the loop.

What is the role of the counter in a counter-based while loop?

A To store the output of the loop

B To stop the program immediately

C To control how many times the loop runs

D To print messages inside the loop

The counter controls the number of loop repetitions by changing each time the loop runs.

What happens if you forget to increase the counter inside a while loop?

A The program will crash immediately

B The loop will run forever (infinite loop)

C The loop will run only once

D The counter will automatically increase

Without increasing the counter, the loop condition never becomes false, causing an infinite loop.

Which of these is a correct way to start a counter for a while loop that runs 5 times?

A All of the above

B int count = 5; while (count > 0) { ... count--; }

C int count = 1; while (count <= 5) { ... count++; }

D int count = 0; while (count < 5) { ... count++; }

All these ways correctly use a counter to run the loop 5 times.

What will this code print? int i = 3; while (i > 0) { System.out.println(i); i--; }

A Nothing

B 1 2 3

C 0 1 2

D 3 2 1

The loop prints 3, then 2, then 1, decreasing i each time until i is 0.

Which part of a counter-based while loop changes each time the loop runs?

A The counter variable

B The loop condition

C The program output

D The loop keyword

The counter variable is updated each time to eventually stop the loop.

Explain how a counter-based while loop works and why the counter must be updated inside the loop.

Think about how the loop knows when to stop.

Write a simple Java while loop that prints numbers from 1 to 5 using a counter.

Start with int i = 1; and use i <= 5 as condition.