undefined array key php

1return $table[$key] ?? null;
2

1function findKey($array, $keySearch)
2{
3    foreach ($array as $key => $item) {
4        if ($key == $keySearch) {
5            echo 'yes, it exists';
6            return true;
7        } elseif (is_array($item) && findKey($item, $keySearch)) {
8            return true;
9        }
10    }
11    return false;
12}
13

1
2<?php
3$array = array(
4    'fruit1' => 'apple',
5    'fruit2' => 'orange',
6    'fruit3' => 'grape',
7    'fruit4' => 'apple',
8    'fruit5' => 'apple');
9
10// this cycle echoes all associative array
11// key where value equals "apple"
12while ($fruit_name = current($array)) {
13    if ($fruit_name == 'apple') {
14        echo key($array).'<br />';
15    }
16    next($array);
17}
18?>
19
20

1<?php
2$array = array(
3    'fruit1' => 'apple',
4    'fruit2' => 'orange',
5    'fruit3' => 'grape',
6    'fruit4' => 'apple',
7    'fruit5' => 'apple');
8
9// this cycle echoes all associative array
10// key where value equals "apple"
11while ($fruit_name = current($array)) {
12    if ($fruit_name == 'apple') {
13        echo key($array).'<br />';
14    }
15    next($array);
16}
17?>