# Arrays and objects

# Indexed arrays

Open course/indexed_arrays.php

TIP

It's common practice to use a plural noun as array variable name (as an array usually contains multiple elements)

Similar to other variabes, arrays don't need to be declared
As in most programming languages, the array indexes start at 0
Arrays can be initialized immediately
- Use an index (between square brackets []) to initialize an array element, as in $students[1] = 'Jane Doe';
- If you initialize an array element without supplying an index, a new array element is added at the end of the array, as in $teachers[] = 'Jan Janssen';
- An array can be initialized at once by putting the element values (seperated by commas) between square brackets [], as in $teachers = [ 'Michaël Cloots' , 'Jan Janssen', 'Patrick Verhaert' ];
  - An alternative (older) way of doing this uses the PHP array() function:
    $teachers = array('Michaël Cloots' , 'Jan Janssen', 'Patrick Verhaert');

REMARKS

As in most programming languages, the array indexes start at 0
The index of the last element equals count(...) - 1

foreach loop

The foreach loop is used to loop over all elements in an indexed array, in an associative array and in an object
There are 2 variants of this loop, depending on whether you want "access" to the values and/or the indexes/keys of the array elements and objects
- foreach ($array as $value){...}
- foreach ($array as $index => $value){...} (on indexed arrays)
- foreach ($array as $key => $value){...} (on associative arrays and objects)

# Associative arrays

Open course/associative_arrays.php

Associative arrays use descriptive strings (e.g. course names) as index or key, as in
- $scoresJohn['PHP'] = 13; to initialize a single element of an associative array
- $scoresJane = ['PHP' => 17, 'Business essentials' => 14, 'English 2' => 10]; to initialize an associative array at once

REMARK

In order to interpolate an element of an associative array in a double quoted (or heredoc) string, it should be wrapped in single curly braces { } to "isolate" it, as in echo "<p> John's score for PHP = {$scoresJohn['PHP']} </p>\n";

Obviously, you can use a concatenated string to generate the same output:
echo "<p> John's score for PHP = " . $scoresJohn['PHP'] . "</p>\n";

# Multidimensional arrays

Open course/multidimensional_arrays.php

<h1>Multidimensional arrays</h1>
<?php
$students = [
   [
       'name' => 'John',
       'scores' => [
           'PHP' => 13, 'Business Essentials' => 8, 'English 2' => 18
       ],
   ],
   [
       'name' => 'Jane',
       'scores' => [
           'PHP' => 17, 'Business Essentials' => 14, 'English 2' => 10
       ],
   ],
   [
       'name' => 'Jeff',
       'scores' => [
           'PHP' => 9, 'Business Essentials' => 11, 'English 2' => 16
       ],
   ],
];
?>

<article>
   <?php
   echo "<p>The name of the first student = {$students[0]['name']}</p>";
   echo "<p>Jeff's score for PHP =  {$students[2]['scores']['PHP']}</p>";
   ?>
</article>

<article>
   <?php
   foreach ($students as $index => $student) {
       echo "<h2> Scores for student $index: {$student['name']} </h2>\n";
       echo "<ul>\n";
       foreach ($student['scores'] as $key => $score) {
           echo "<li>{$student['name']}'s score for $key = $score </li>\n";
       }
       echo "</ul>\n<hr>\n";
   }
   ?>
</article>

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43

Multidimensional arrays

A multidimensional array is a (nested) array that stores another array at each index (instead of a single element)
- Both indexed and associative two-dimensional arrays are possible
- Use 2 or more pairs of square brackets [][] to identify a specific element

# Objects

Open course/objects.php

<h1>Objects</h1>
<?php
$students = [
    [
        'name' => 'John',
        'scores' => [
            'PHP' => 13, 'Business Essentials' => 8, 'English 2' => 18
        ],
    ],
    [
        'name' => 'Jane',
        'scores' => [
            'PHP' => 17, 'Business Essentials' => 14, 'English 2' => 10
        ],
    ],
    [
        'name' => 'Jeff',
        'scores' => [
            'PHP' => 9, 'Business Essentials' => 11, 'English 2' => 16
        ],
    ],
];

// convert array to object
$studentsObj = json_decode(json_encode($students));

foreach ($studentsObj as $index => $student) {
    echo "<article>\n";
    echo "<h2> Scores for student $index: $student->name </h2>\n";
    echo "<ul>\n";
    foreach ($student->scores as $key => $score) {
        echo "<li>{$student->name}'s score for $key = $score </li>\n";
    }
    echo "</ul>\n";
    echo "</article>\n";
}
?>
</article>

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38

Objects

For simple, associative arrays, it's probably sufficient to cast the array to an object: $object = (object) $array;, but this does not work for multidimensional arrays!
The cleanest solution is to use the built-in json_ functions: $object = json_decode(json_encode($array), false);
- You can omit the second parameter of json_decode if it is false
- Set the second parameter of json_decode to true to convert an object back to an associative array

# Debugging tips

The PHP functions var_dump() and print_r() both show information (content) about a variable on screen
TIP: wrap the function call in a <pre> tag to preserve the formatting of the output