AP CSA 2.8 Exercise 2: for Loops Applied Practice

Unit 2: Selection and Iteration · Lesson 2.8 · Exercise 2

for Loops: Applied Practice

Six scenarios on the three parts of a for header and exactly how many times the body runs.

Back to the Lesson 2.8 pageAll Unit 2 lessons

How this one is different

The exercise-1 editor asks you to write for loops. These six are mostly counting, because off-by-one is the error that survives testing on the happy path.

Applied Practice

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

Question 1 of 6Apply
A loop reads for (int i = 1; i <= n; i++).
How many times does the body execute?
Correct. Correct. Starting at 1 with <= n gives exactly n passes.
Incorrect. That would need starting at 0 with <= n.
Incorrect. The body cannot change the count unless it alters i or breaks.
Incorrect. That would be the count for i < n.
Question 2 of 6Analyze
A loop reads for (int i = 0; i < n; i++) and a student changes < to <=.
What is the consequence when the body indexes an array of length n?
Incorrect. The iteration count changes by one.
Incorrect. It still terminates, just one pass too late.
Incorrect. The change adds a pass rather than removing one.
Correct. Correct, and it is the single most common runtime error in the course.
Question 3 of 6Apply
A for loop declares its counter in the header: for (int i = 0; ...).
What is true after the loop finishes?
Incorrect. An int is never null.
Incorrect. That requires declaring i before the loop.
Correct. Correct, and needing the final value is the usual reason to declare it outside.
Incorrect. Nothing resets it; it simply ceases to exist.
Question 4 of 6Analyze
A for loop is written with an empty condition: for (int i = 0; ; i++).
What happens?
Incorrect. All three header parts are optional.
Correct. Correct, and it is only useful with a break inside.
Incorrect. Nothing stops it after one pass.
Incorrect. A missing condition never blocks entry.
Question 5 of 6Evaluate
A loop counts down: for (int i = n; i > 0; i--).
Which values does i take in the body?
Correct. Correct: n passes, ending at 1.
Incorrect. The loop starts at n, not n - 1.
Incorrect. It decrements through the whole range.
Incorrect. The condition i > 0 excludes 0.
Question 6 of 6Apply
A student modifies the loop counter inside the body of a for loop as well as in the header.
What is the risk?
Incorrect. Both updates apply, compounding each other.
Incorrect. The effect depends entirely on what the body does.
Incorrect. It is legal, which is why it is a hazard rather than an error.
Correct. Correct. The header stops being a reliable summary of what the loop does.

Where to go next

Try the Lesson 2.8 coding exercise Pick another Unit 2 lesson

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