AP® Computer Science Principles Free-Response Questions Past Paper 2025 Solution

Task: Three parts: 1) Identify the Boolean expression. 2) Identify values that make it `false`. 3) Explain *why* those values make it `false`.

Planning for the "Study Buddy Quiz" App:

1. Boolean Expression: The expression is (userAnswer == questionBank[questionIndex].correctAnswer).
2. Values for `false`: This is simple. The user's answer just needs to not match the correct answer. Let's say the current question's correct answer is "A". So, questionBank[questionIndex].correctAnswer has the value "A". The user inputs "B", so userAnswer has the value "B".
3. Explanation: The comparison operator == checks for equality. The expression becomes "B" == "A". Since the string "B" is not equal to the string "A", the expression evaluates to `false`.

Task: Two parts: 1) Describe a modification to the list traversal code segment that causes a logic error. 2) Explain why it's a logic error.

Planning for the "Study Buddy Quiz" App:

1. Identify the code segment: The list traversal is in the calculateFinalScore() loop, which iterates through resultsList. Let's imagine the code looks like this:
   score = 0
FOR EACH result IN resultsList {
IF (result == true) {
score = score + 1
}
}
2. Describe a modification: A common logic error in loops is an "off-by-one" error or incorrect initialization. A programmer could mistakenly initialize the score incorrectly. For example, they could change score = 0 to score = 1 before the loop begins.
3. Explain the logic error: This is a logic error because the code will still run without crashing, but it will produce an incorrect final score. The score should start at 0 before any correct answers are counted. By starting the score at 1, the final calculated score will always be one point higher than the user actually earned. For a user who gets 7 out of 10 questions correct, the program would incorrectly report their score as 8.

Task: Three parts: 1) Describe the functionality of the procedure. 2) Explain how using a procedure makes the program easier to maintain. 3) Contrast this with not using a procedure.

Planning for the "Study Buddy Quiz" App:

1. Describe functionality: The procedure is checkAnswer(userAnswer, questionIndex). Its functionality is to determine if a user's submitted answer for a specific question is correct. It takes the user's answer and the question's index as input, compares the input to the correct answer stored in the questionBank list, and then updates the user's score and provides feedback accordingly.
2. Explain benefit of procedure (maintenance): Procedures (abstractions) make programs easier to maintain because they encapsulate a specific piece of functionality. If I need to change how an answer is checked (e.g., make it case-insensitive, or award partial credit), I only have to modify the code inside the checkAnswer procedure. All the parts of my program that call this procedure will automatically use the updated logic without needing to be changed themselves.
3. Contrast with no procedure: If I had *not* used a procedure, I would have had to copy and paste the answer-checking code for every single question in my quiz. If my quiz had 10 questions, that's 10 blocks of nearly identical code. If I then decided to change the scoring logic, I would have to find and modify all 10 of those blocks individually. This would be time-consuming, tedious, and highly prone to errors (e.g., forgetting to update one of the blocks), making the program much harder to maintain and debug.