如果条件在PHP奇怪的情况

Question

I have found a strange situation in php...or maybe I don't remember something well:

<?php

if (isset($_POST["invio"]) && ($_POST["valore1"] && $_POST["valore2"])) {

        if($_POST["valore1"]) {
        $valore1 = $_POST["valore1"];
        }
        if($_POST["valore2"]) {
        $valore2 = $_POST["valore2"];
        }


        function pippo ($x,$y) {

        if($x < $y) {
        return "la variabile $x è minore della variabile $y";
        }
        elseif($x == $y) {
        return "la variabile $x è uguale alla variabile $y";
        }
        else {
        return "la variabile $x è più grande rispetto alla variabile $y";
        }
        }

        $risultato = pippo($valore1,$valore2);

        print $risultato;

}elseif (isset($_POST["invio"]) && ($_POST["valore1"] =="" || $_POST["valore2"] =="") ) {
        print "Manca almeno un valore";
        }

If I try to delete the two parentheses:

}elseif (isset($_POST["invio"]) && $_POST["valore1"] =="" || $_POST["valore2"] =="" ) {
        print "Manca almeno un valore";
        }

The system enters inside the condition with the print.. why does it do this?

Answer 1

AND has higher precedence than OR so

a && b || c

is interpreted as

(a && b) || c

Not as

a && (b || c)

AND is the boolean version of multiplication -- (0 AND 1) is 0 just like (0 * 1) is 0.

OR is like addition -- (0 OR 1) is 1 just as (0 + 1) is 1.

A * B + C would also be understood as (A * B) + C.