PHP foreach loop can be used with Indexed arrays, Associative arrays and Object public variables.
In foreach loop, the first thing php does is that it creates a copy of the array which is to be iterated over. PHP then iterates over this new copy of the array rather than the original one. This is demonstrated in the below example:
<?php
$numbers = [1,2,3,4,5,6,7,8,9]; # initial values for our array
echo '<pre>', print_r($numbers, true), '</pre>', '<hr />';
foreach($numbers as $index => $number){
$numbers[$index] = $number + 1; # this is making changes to the origial array
echo 'Inside of the array = ', $index, ': ', $number, '<br />'; # showing data from the copied array
}
echo '<hr />', '<pre>', print_r($numbers, true), '</pre>'; # shows the original values (also includes the newly added values).
Besides this, php does allow to use iterated values as a reference to the original array value as well. This is demonstrated below:
<?php
$numbers = [1,2,3,4,5,6,7,8,9];
echo '<pre>', print_r($numbers, true), '</pre>';
foreach($numbers as $index => &$number){
++$number; # we are incrementing the original value
echo 'Inside of the array = ', $index, ': ', $number, '<br />'; # this is showing the original value
}
echo '<hr />';
echo '<pre>', print_r($numbers, true), '</pre>'; # we are again showing the original value
Note: It does not allow original array indexes to be used as references.
Source: http://dwellupper.io/post/47/understanding-php-foreach-loop-with-examples