JuniorTheoryCommon

What does the program print?

PHP

<?php

$a = [1, 2, 3];
$b = $a;
$b[] = 4;
$b[0] = 100;
echo count($a), ' ', $a[0], ' ', count($b), ' ', $b[0], "\n";

3 1 4 100

Expecting $b to be a second name for the same array, as in Python or JavaScript: in PHP $b = $a copies the array, so $a keeps [1, 2, 3].
Expecting some writes to $b to show up in $a: after $b = $a the arrays are independent, so neither $b[] = 4 nor $b[0] = 100 changes $a.

JuniorTheoryCommon

PHP

<?php

$a = [1, 2, 3];
$b = $a;
$b[] = 4;
$b[0] = 100;
echo count($a), ' ', $a[0], ' ', count($b), ' ', $b[0], "\n";

3 1 4 100

Expecting $b to be a second name for the same array, as in Python or JavaScript: in PHP $b = $a copies the array, so $a keeps [1, 2, 3].
Expecting some writes to $b to show up in $a: after $b = $a the arrays are independent, so neither $b[] = 4 nor $b[0] = 100 changes $a.