Description:
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The substr() function will convert an integer and return the correct results.  Using strlen() returns NULL, it does not convert an integer to string so that the expected results are returned.

Reproduce code:
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$string = '12345';
$number = 12345;
print substr($number, -1) . '<br />'; // works fine
print $string{strlen($string)-1} . '<br />'; works fine
// This won't work, $number is not a string:
print $number{strlen($number)-1} . '<br />';
// Now cast it as a string and it will:
$number = (string)$number;
print $number{strlen($number)-1} . '<br />';


Expected result:
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I would expect PHP to automagically convert the integer to a string without having to cast it as string first.