AP CSA 4.1 Debugging: Reporting More Than You Should

Unit 4: Data Collections · Lesson 4.1 · Debugging

Reporting More Than You Should

Ethical and Social Issues Around Data Collection. This is not a blank editor: it is someone else's attempt. Find what is wrong, fix it, and submit to be graded against hidden test cases.

Back to the Lesson 4.1 page All Unit 4 lessons

Why debugging is its own skill

This program aggregates survey responses, and it leaks. It publishes a group average computed from a single person, which identifies that person exactly, and it echoes a raw record it was only ever supposed to count. Both are real privacy failures and both look like ordinary code.

What is wrong with it

A group containing only one response must be suppressed rather than reported, because an average over one person IS that person's answer. Print SUPPRESSED for any group with fewer than 2 responses instead of the average.
The program prints the first raw response value back out. It was only supposed to report counts and averages. Remove that line so no individual record is echoed.
The total count line is fine to publish and should stay.

The program reads

A group size, then that many integer responses.

The program should print

Two lines: the number of responses, then the integer average, or SUPPRESSED when the group is too small to report.

Worked examples

These show what the FIXED program should print. There are more cases you cannot see, and they use different values, so patching around just these numbers will fail.

Example 1 input

1
7

Example 1 output

1
SUPPRESSED

Example 2 input

4
10 20 30 40

Example 2 output

4
25

Your answer

Main.java

import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    int n = input.nextInt();
    int[] responses = new int[n];
    for (int i = 0; i < n; i++) {
      responses[i] = input.nextInt();
    }

    int total = 0;
    for (int r : responses) {
      total = total + r;
    }

    System.out.println(n);
    System.out.println(responses[0]);
    System.out.println(total / n);
  }
}

Input for the Run button

Run sends whatever is in the code box below, bugs and all, so you can see the crash or the wrong answer for yourself before you fix anything.

Stuck?

Hint 1

An average over one value is not anonymous in any sense: it is that value, republished with a label that sounds statistical. Real data releases use a minimum group size for exactly this reason, and 2 is the smallest one that means anything.

Hint 2

The line printing responses[0] is not a debugging leftover to keep. Publishing one raw record is the same disclosure the aggregate was designed to prevent.

Hint 3

The count itself is safe to publish. Knowing that six people answered tells you nothing about what any one of them said.

Where to go next

Rework the Lesson 4.1 page Try the from-scratch version of this lesson

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