array_push()
array_push() adds the second argument, and all the next, to the end of the array, passed as first argument. A new index is created for each new entry, in order.
array_push() adds the new elements and creates the new keys. It is not possible to specify a key with this function: one should use the $array['key'] = $value syntax.
array_pop() is the equivalent operation of the [] append operator. It is the opposite of array_push(). With these functions, it is possible to build FIFO stack.
<?php
$array = [0, 1, 2];
print array_push($array, 3, 4); // 5, the number of elements
// $array == [0, 1, 2, 3, 4];
$array = [0, 1, 2];
$array[] = 3;
// $array == [0, 1, 2, 3];
$array = [0, 1, 2];
$array[33] = 3;
// $array == [0, 1, 2, 33 => 3];
?>