How do I use or operator in PHP?

Question

if($a=="" and $b=="" or $c=="") {
    echo "something";
}

I want to ask that if $a AND $b is empty then it will print: something. But if $b is not empty, then it will check the statement like this e.g. if $a is empty AND $c is empty then print: something (Means $a is compulsory to check with the variable which is empty $b OR $c)

@Rizier123 This isn't about using the spelled out names versus the operators. This question relates to precedence between `and` and `or`. He'd have the same problem if he used `&&` and `||`, he would still need parentheses. — Barmar, Apr 16 '15 at 20:12

score 1 · Answer 1 · edited May 23 '17 at 12:14

See the PHP Operator Precedence table. and has higher precedence than or, so your condition is treated as if you'd written

if (($a == "" and $b == "") or ($c == ""))

Since you want the $a check to be independent, you need to use parentheses to force different grouping:

if ($a == "" and ($b == "" or $c == ""))

Note that in expressions, it's conventional to use && and || rather than and and or -- the latter are usually used in assignments as a control structure, because they have lower precedence than assignments. E.g.

$result = mysqli_query($conn, $sql) or die (mysqli_error($conn));

See 'AND' vs '&&' as operator

AbraCadaver · Answer 2 · 2015-04-16T20:20:44.483

0

Just force the comparison order/precedence by using parentheses:

if( $a == "" and ( $b == "" or $c == "" ) )

But you would be better off using && and ||:

if( $a == "" && ( $b == "" || $c == "" ) )

edited Apr 16 '15 at 20:20

answered Apr 16 '15 at 20:07

AbraCadaver

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I'd say this does _not_ implement the described logic. – arkascha Apr 16 '15 at 20:11
@arkascha: And you can describe the logic based on _MEANS $a IS COMPULSORY TO CHECK WITH THE VARIABLE WHICH IS EMPTY $b or $c_ – AbraCadaver Apr 16 '15 at 20:12
Sorry, but this would also resolve to `true` if `$a` is _not_ empty, but `$c` is. – arkascha Apr 16 '15 at 20:19

Iłya Bursov · Answer 3 · 2015-04-16T20:10:28.493

0

I suppose you need something like this:

if (
    ($a == '')
    &&
    (
        ($b == '')
        ||
        ($c == '')
    )
   )

so, it will print something only when $a is empty and either $b or $c empty

edited Apr 16 '15 at 20:10

answered Apr 16 '15 at 20:08

Iłya Bursov

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I would call this "questionable indentation" :-) However the logic is correct. – arkascha Apr 16 '15 at 20:09
@arkascha indentation is only to show logic and priorities – Iłya Bursov May 12 '15 at 14:32

How do I use or operator in PHP?

3 Answers3