var_dump(0 == 'all'); // WHY TRUE

Question

I don't understand below output . found below expressions on php.net manual in boolean section.

<?php

    var_dump(0 == 'all');//   IS bool(true)
    var_dump((string)0 == 'all');  //IS bool(false)
    var_dump(0 === 'all'); // //IS bool(false)

?>

Answer 1

If you compare an integer with a string, each string is converted to a number, so:

(0 == 'all') -> (0 == 0) -> true

The type conversion does not happen when the comparison is === or !== because this also includes the comparison of the type:

(0 === 'all') -> (integer == string) -> false

The second line of code you wrote force the integer value to be considered as a string, and so the numerical cast doesn't happen.