if statement - Why does (0 == 'Hello') return true in PHP?

Question

Hey, if you have got the following code and want to check if $key matches Hello I've found out, that the comparison always returns true if the variable is 0. I've came across this when an array for a special key and wondered why it's wasn't working as expected. See this code for an example.

$key = 1;
if ($key != 'Hello') echo 'Hello'; //echoes hello

$key = 2;
if ($key != 'Hello') echo 'Hello'; //echoes hello

$key = 0;
if ($key != 'Hello') echo '0Hello'; //doesnt echo hello. why?
if ($key !== 'Hello') echo 'Hello'; //echoes hello

Can anyone explain this?

Answer 1

The operators == and != do not compare the type. Therefore PHP automatically converts 'Hello' to an integer which is 0 (intval('Hello')). When not sure about the type, use the type-comparing operators === and !==. Or better be sure which type you handle at any point in your program.