Activity 5.4 — Parallel Arrays

Introduction

Activity 5.4

Parallel Arrays

The Big Idea

Parallel arrays store related information in separate arrays. The relationship is maintained by using the same index.

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// Parallel arrays = same index = same "record"
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names[i]  <->  scores[i]

Think Like a “Record”

If names[2] is "Sam"...
...then scores[2] is Sam's score.
Same index = same person / same item.

Traversal Must Stay in Sync

When you loop, you loop over the indexes and use both arrays.

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// Traverse IN SYNC
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for (int i = 0; i < names.length; i++)
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{
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    System.out.println(names[i] + ": " + scores[i]);
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}

Common Algorithm: “Best So Far”

Often you don't store the best value — you store the index of the best value. Then you can use that index in both arrays.

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// Find the index of the best score, then use it
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int bestIndex = 0;
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for (int i = 1; i < scores.length; i++)
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{
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    if (scores[i] > scores[bestIndex])
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    {
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        bestIndex = i;
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    }
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}
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// names[bestIndex] matches scores[bestIndex]

Common Algorithm: Search by Name

To find a student, you search the names array. If you find it, you use the same index to get the score.

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// Linear search across a parallel array
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int index = -1;
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for (int i = 0; i < names.length; i++)
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{
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    if (names[i].equals(targetName))
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    {
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        index = i;
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    }
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}

If the name is not found, keep index as -1.

Today's Two Apps

Numeric App: Score Analyzer (average, max, passing count, lookup)
Quiz App: Questions + Answers using parallel arrays

Success Criteria

You can explain what “same index” means.
Your loops keep arrays aligned.
You can find and use the correct index for calculations and search.

'F' → Fullscreen

Objectives

Explain how parallel arrays store related data using matching indexes.
Traverse two arrays in sync to print, compute, and analyze data.
Use linear search on one array and use the found index to access the other.
Build two small apps that use parallel arrays: a numeric analyzer and a quiz.

Activity Tasks

Create a new project named Activity5-4-ParallelArrays.
Complete both tasks.

Task 1: Numeric App — Student Score Analyzer

Print a roster (name + score) using one loop.
Compute and print the class average.
Find and print the top student's name and score.
Count and print how many students are passing (>= 70).
Ask the user for a name and print that student's score (or “Not found”).

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import java.util.Scanner;
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public class Program
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{
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    public static void main(String[] args)
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    {
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        // Task 1 — Numeric App: Student Score Analyzer (Parallel Arrays)
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        //
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        // You are given two parallel arrays:
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        // - names[i] goes with scores[i]
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        //
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        // Your job:
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        // 1) Print a roster (each student + score)
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        // 2) Compute and print the class average
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        // 3) Find and print the highest score AND the student's name
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        // 4) Count and print how many students are passing (>= 70)
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        // 5) Ask the user for a name and print that student's score (or "Not found")
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        String[] names = {"Ava", "Ben", "Chris", "Dina", "Eli"};
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        int[] scores = {88, 73, 95, 67, 81};
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        // 1) Print roster
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        System.out.println("Roster:");
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        for (int i = 0; i < names.length; i++)
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        {
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            System.out.println(names[i] + ": " + scores[i]);
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        }
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        // 2) Average
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        int sum = 0;
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        for (int i = 0; i < scores.length; i++)
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        {
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            sum += scores[i];
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        }
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        double avg = (double) sum / scores.length;
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        System.out.println("Average: " + avg);
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        // 3) Highest score + name
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        int bestIndex = 0;
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        for (int i = 1; i < scores.length; i++)
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        {
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            if (scores[i] > scores[bestIndex])
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            {
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                bestIndex = i;
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            }
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        }
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        System.out.println("Top student: " + names[bestIndex]);
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        System.out.println("Top score: " + scores[bestIndex]);
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        // 4) Count passing (>= 70)
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        int passing = 0;
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        for (int i = 0; i < scores.length; i++)
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        {
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            if (scores[i] >= 70)
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            {
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                passing++;
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            }
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        }
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        System.out.println("Passing count: " + passing);
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        // 5) Search by name
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        Scanner scanner = new Scanner(System.in);
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        System.out.print("Enter a student name to look up: ");
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        String targetName = scanner.nextLine();
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        int index = -1;
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        for (int i = 0; i < names.length; i++)
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        {
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            if (names[i].equals(targetName))
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            {
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                index = i;
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            }
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        }
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        if (index == -1)
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        {
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            System.out.println("Not found.");
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        }
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        else
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        {
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            System.out.println(targetName + "'s score: " + scores[index]);
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        }
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        scanner.close();
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    }
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}

Task 2: Quiz App — Questions + Answers

Ask each question in a loop.
Compare answers using equalsIgnoreCase.
Track a score counter and print the final score.
Print feedback after each question.

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import java.util.Scanner;
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public class Program
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{
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    public static void main(String[] args)
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    {
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        // Task 2 — Quiz App: Question + Answer Parallel Arrays
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        //
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        // You are given two parallel arrays:
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        // - questions[i] goes with answers[i]
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        //
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        // Your job:
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        // 1) Ask each question
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        // 2) Compare the user's answer to the correct answer (case-insensitive)
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        // 3) Keep score and print the final result
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        //
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        // Notes:
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        // - Use equalsIgnoreCase(...) for comparison
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        // - Print "Correct!" or "Incorrect. The answer was ___"
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        String[] questions =
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        {
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            "What is 2 + 2?",
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            "What keyword starts a for loop in Java?",
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            "What is the first index in an array?",
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            "True/False: Arrays can change size after creation."
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        };
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        String[] answers =
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        {
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            "4",
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            "for",
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            "0",
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            "false"
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        };
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        Scanner scanner = new Scanner(System.in);
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        int correct = 0;
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        System.out.println("Quiz Time!");
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        System.out.println("----------");
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        for (int i = 0; i < questions.length; i++)
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        {
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            System.out.println("Q" + (i + 1) + ": " + questions[i]);
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            System.out.print("Your answer: ");
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            String user = scanner.nextLine();
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            if (user.equalsIgnoreCase(answers[i]))
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            {
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                System.out.println("Correct!");
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                correct++;
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            }
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            else
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            {
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                System.out.println("Incorrect. The answer was: " + answers[i]);
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            }
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            System.out.println();
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        }
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        System.out.println("Final Score: " + correct + " / " + questions.length);
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        scanner.close();
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    }
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}

Sample Output

Your program output should something similar to the sample output below.

Roster:
Ava: 88
Ben: 73
Chris: 95
Dina: 67
Eli: 81
Average: 80.8
Top student: Chris
Top score: 95
Passing count: 4
Enter a student name to look up: Dina
Dina's score: 67

Quiz Time!
----------
Q1: What is 2 + 2?
Your answer: 4
Correct!

Q2: What keyword starts a for loop in Java?
Your answer: for
Correct!

Q3: What is the first index in an array?
Your answer: 1
Incorrect. The answer was: 0

Q4: True/False: Arrays can change size after creation.
Your answer: false
Correct!

Final Score: 3 / 4

Reflection Questions

You may write your reflection answers as comments at the bottom of your code.

In your own words, what does “same index = same record” mean?
Why is it safer to store bestIndex instead of storing the best score directly?
What does the value -1 mean in a search algorithm?
What could go wrong if two parallel arrays are not the same length?

Submission

Submit your activity and reflection answers to the appropriate dropbox.