Challenge 1 — Solution

Task: Create an associative array representing a book with keys
"title", "author", and "year". Echo a formatted sentence using all
three values, then add a new key "genre" and echo the whole array with
print_r.

<?php
    $book = [
        "title" => "The Pragmatic Programmer",
        "author" => "David Thomas",
        "year" => 1999
    ];

    echo $book["title"] . " by " . $book["author"] . " (" . $book["year"] . ")<br>";

    $book["genre"] = "Software Engineering";
    print_r($book);
?>


Output:
The Pragmatic Programmer by David Thomas (1999)
Array
(
    [title] => The Pragmatic Programmer
    [author] => David Thomas
    [year] => 1999
    [genre] => Software Engineering
)

Notes:
- Each value is accessed with its own named key rather than a numeric
  position, e.g. $book["title"] rather than $book[0].
- Assigning to a key that doesn't exist yet ($book["genre"] = ...)
  simply adds it to the array - no special "add a new key" syntax is
  needed beyond a normal assignment.
- print_r() shows every key-value pair in the array in a readable
  format, confirming the new "genre" key was added successfully
  alongside the original three.