AP CSA 2.1 Exercise 2: Algorithms with Selection and Repetition Applied Practice

Unit 2: Selection and Iteration · Lesson 2.1 · Exercise 2

Algorithms with Selection and Repetition: Applied Practice

Six scenarios on recognizing which control structure a problem actually needs before any code is written.

How this one is different

The exercise-1 editor asks you to build an algorithm. These six ask you to pick the shape first, which is the decision that makes the rest either easy or impossible.

Applied Practice

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

Question 1 of 6Apply
A program must apply a discount only to orders over 50 dollars, and each order is processed once.
Which control structure does this require?
Incorrect. Nothing repeats. One order is examined one time.
Correct. Correct. A decision with no repeated work is exactly what selection is for.
Incorrect. Nesting solves a problem this scenario does not have.
Incorrect. Plain sequence cannot skip the discount for small orders.
Question 2 of 6Analyze
A program must keep prompting a user until they enter a valid password, with no fixed limit on attempts.
Which structure fits?
Correct. Correct. Condition-controlled repetition is the defining case for while.
Incorrect. An if checks once. It cannot re-prompt.
Incorrect. Nothing here iterates over characters.
Incorrect. The attempt count is not known in advance, which is what a for loop assumes.
Question 3 of 6Apply
An algorithm must print a grade letter for each of exactly 30 students.
What combination is needed?
Incorrect. Choosing among letters is itself a decision and needs selection.
Incorrect. A fixed count is exactly when a for loop applies, not when repetition becomes unnecessary.
Incorrect. Writing the decision out 30 times is what the loop exists to avoid.
Correct. Correct. A per-item decision inside a traversal is the most common structure in the course.
Question 4 of 6Evaluate
A student claims that any algorithm using a while loop can be rewritten with a for loop.
Is that accurate?
Incorrect. For an unknown number of attempts, a for loop obscures the intent.
Incorrect. They are interchangeable in capability.
Correct. Correct. The real distinction is which one states the intent, not which one can do the job.
Incorrect. The middle part of a for header IS a condition.
Question 5 of 6Analyze
An algorithm must find whether ANY value in a list is negative.
What is the minimum work required?
Incorrect. Only necessary when no negative exists.
Correct. Correct, and the mirror image is a universal claim, which is settled by one counterexample.
Incorrect. Sorting is far more work than a single scan.
Incorrect. Counting every negative computes more than the question asked.
Question 6 of 6Apply
Two algorithms solve the same problem. One uses a single loop; the other uses a loop nested inside a loop.
What does that structural difference usually signal?
Correct. Correct, and this is the intuition 2.12 formalizes as informal run-time analysis.
Incorrect. Nesting adds passes, not storage.
Incorrect. The difference grows with input size and can be dramatic.
Incorrect. Nesting is required for genuinely two-dimensional problems.

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