AP CSA 2.7 Exercise 2: while Loops Applied Practice

Unit 2: Selection and Iteration · Lesson 2.7 · Exercise 2

while Loops: Applied Practice

Six scenarios on what makes a loop stop, and the three separate ways one fails to.

Back to the Lesson 2.7 pageAll Unit 2 lessons

How this one is different

The exercise-1 editor asks you to write a while loop. These six ask what advances it toward termination, since a loop that never ends produces no output to debug from.

Applied Practice

6 questions · scenario driven · every answer is recorded for your teacher

Question 1 of 6Analyze
A while loop reads a value from input and never modifies its own counter inside the body.
Under what condition does it still terminate?
Incorrect. Java imposes no iteration limit.
Incorrect. It runs as long as the condition holds.
Incorrect. Too strong. Progress can come from outside the loop body.
Correct. Correct. What matters is that SOMETHING in the condition changes, not specifically a counter.
Question 2 of 6Apply
A sentinel loop should stop when the user enters -1, written as while (input != -1).
Where must the next read happen?
Incorrect. Reading inside a condition is legal in some languages but obscures the flow and is not the taught pattern.
Incorrect. Then the condition tests the same value forever.
Correct. Correct. The priming read plus the update read is the standard sentinel shape.
Incorrect. The first test would run against an uninitialized or stale value.
Question 3 of 6Analyze
A loop is written while (i < 10) with i incremented by 2 starting from 1.
How many times does the body run?
Incorrect. Ten would require a step of 1 from 0.
Correct. Correct: the odd values below 10.
Incorrect. Undercounts by one; 9 is still less than 10.
Incorrect. That counts every value, not every other one.
Question 4 of 6Apply
A loop must run at least once before its condition is checked.
Which structure fits?
Correct. Correct. Guaranteed first execution is exactly what do-while provides.
Incorrect. A for loop still tests before the first pass.
Incorrect. That adds a decision without changing when the loop tests.
Incorrect. That never stops without an added break.
Question 5 of 6Evaluate
A while loop's condition compares a double accumulated by repeated addition against an exact value.
Why might it fail to terminate?
Incorrect. Speed has no bearing on termination.
Incorrect. Binary floating point cannot represent many decimal values exactly.
Incorrect. They can; exact equality is the unreliable part.
Correct. Correct, and the fix is a relational test rather than an equality test.
Question 6 of 6Apply
A loop should stop early when a condition is met, but the surrounding method must still run cleanup afterward.
What is the appropriate mechanism?
Incorrect. That terminates the whole program.
Incorrect. Returning skips the cleanup the method still owes.
Correct. Correct. break exits the loop only.
Incorrect. continue keeps looping rather than leaving.

Where to go next

Try the Lesson 2.7 coding exercise Pick another Unit 2 lesson

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