This simple script illustrates that PHP interprets digits with leading zeros as an octal. This can cause problems when interpreting user input as an integer without converting it to a string first then parsing it (e.g with intval()).

php_leading_zero_numbers.php

<?php
echo 'This simple script illustrates that PHP interprets digits with leading zeros as an octal. This can cause problems when interpreting user input as an integer without converting it to a string first then parsing it (e.g with intval()).';
echo '<br>Notice that numbers greater than 7 do not compare nicely with their leading-zero counterparts.';
echo '<br>';
echo '9';
echo '<br>';
echo '9==09 ... ';
echo iif(9==09, 'true', 'false');
echo '<br>';
echo '9==9 ... ';
echo iif(9==9, 'true', 'false');
echo '<br>';
echo '<br>';
echo '8';
echo '<br>';
echo '8==08 ... ';
echo iif(8==08, 'true', 'false');
echo '<br>';
echo '8==8 ... ';
echo iif(8==8, 'true', 'false');
echo '<br>';
echo '8 compared to octal "010"';
echo '<br>';
echo '8==010 ... ';
echo iif(8==010, 'true', 'false');
echo '<br>';
echo '<br>';
echo '7';
echo '<br>';
echo '7==07 ... ';
echo iif(7==07, 'true', 'false');
echo '<br>';
echo '7==7 ... ';
echo iif(7==7, 'true', 'false');
echo '<br>';
echo '<br>';
echo '6';
echo '<br>';
echo '6==06 ... ';
echo iif(6==06, 'true', 'false');
echo '<br>';
echo '6==6 ... ';
echo iif(6==6, 'true', 'false');
echo '<br>';
echo '<br>';
echo '5';
echo '<br>';
echo '5==05 ... ';
echo iif(5==05, 'true', 'false');
echo '<br>';
echo '5==5 ... ';
echo iif(5==5, 'true', 'false');
echo '<br>';
echo '<br>';
echo '4';
echo '<br>';
echo '4==04 ... ';
echo iif(4==04, 'true', 'false');
echo '<br>';
echo '4==4 ... ';
echo iif(4==4, 'true', 'false');
echo '<br>';
echo '<br>';
echo '3';
echo '<br>';
echo '3==03 ... ';
echo iif(3==03, 'true', 'false');
echo '<br>';
echo '3==3 ... ';
echo iif(3==3, 'true', 'false');
echo '<br>';
echo '<br>';
echo '2';
echo '<br>';
echo '2==02 ... ';
echo iif(2==02, 'true', 'false');
echo '<br>';
echo '2==2 ... ';
echo iif(2==2, 'true', 'false');
echo '<br>';
echo '<br>';
echo '1';
echo '<br>';
echo '1==01 ... ';
echo iif(1==01, 'true', 'false');
echo '<br>';
echo '1==1 ... ';
echo iif(1==1, 'true', 'false');
echo '<br>';
echo '<br>';

function iif($test,$test_true_result,$test_false_result='') {
   return $test ? $test_true_result : $test_false_result;
}
?>