Challenge - Array operations

Build a student grade board with associative arrays, foreach and array methods.

Challenge - Array operations

In this challenge you'll build a student grade board. You'll store two classes' grades as associative arrays, merge them with array_merge and use foreach to compute and print each student's average.

Each student's value is an array of scores; with a nested foreach you sum them and divide by count. This combines associative arrays, loops and arithmetic.

Exercise Build the grade board

Add "Alex" => [80, 90, 100] and "Maya" => [70, 80, 90] to the $grades1 associative array. Add "Sam" => [90, 100, 95] to $grades2. Merge with $all = array_merge($grades1, $grades2). Walk each student with an outer foreach ($all as $name => $scores); sum the scores with an inner foreach ($scores as $score); compute $avg = $total / count($scores); print echo $name . ": " . $avg . "\n".

Show example solution

Define $grades1 and $grades2 associative arrays; merge with array_merge; outer foreach walks key value, inner foreach walks scores; average = total / count.
Example solution:
<?php
// Student grade board: array_merge and two foreach loops
$grades1 = [
    "Alex" => [80, 90, 100],
    "Maya" => [70, 80, 90],
];
$grades2 = [
    "Sam" => [90, 100, 95],
];
$all = array_merge($grades1, $grades2);

foreach ($all as $name => $scores) {
    $total = 0;
    foreach ($scores as $score) {
        $total += $score;
    }
    $avg = $total / count($scores);
    echo $name . ": " . $avg . "\n";
}

Test yourself

How does array_merge($a, $b) behave with associative arrays?
- It deletes common keys
- It merges the values of common keys
- The second array's value wins for common keys
- It cannot merge associative arrays
Show answer

The second array's value wins for common keys — Correct. In array_merge, when the same string key exists, the second array's value overwrites the first.

Complete the outer loop

foreach ($all ____ $name => $scores) {
    // inner loop and average
}

Show answer

foreach ($all as $name => $scores) {
    // inner loop and average
}

Match the array concepts

array_merge

merges arrays
foreach

iterates array
count

element count
$scores as $score

inner loop

Next lesson: Challenge - Functions and loops

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