php why does or operator return 0 as true

Question

In the following code:

$a = 0 or 1;
$b = 0 || 1; 
echo "$a, $b"; // 0, 1

Why does $a equal zero, I thought or and || were interchangeable in PHP? What exactly is going on with the or statement to make it return 0?

I would have assume both results would have been 1 making it echo 1, 1.

Answer 1

or is lower precedence than = which is lower precedence than ""

So your code is equivalent to:

($a = 0) or 1;
$b = (0 || 1); 

See the precedence table in the PHP manual.