print_r() is not helpful (in most cases, but especially for debugging) as it hides useful information from you. observe:

print_r_lies.php

<?php

$a = [
    "true",
    true,
    1,
    "1",
    "false",
    false,
    0,
    "0",
    "a string",
    "a string                                                                        ",
    "a \x00\x00\x00string",
    "Array
    (
        [0] => a
        [1] => b
        [2] => c
    )",
    "a string
    [13] => Array
    (
        [0] => yeah, this is in fact still the same string as [12]
    )"
];

header("Content-type: text/plain");
print_r($a);
var_dump($a);