CODEWITHSUNDEEP
phpoperatorslogical-operatorsor-operator
ItsPronounced
ItsPronounced

Reputation: 5463

Logical Operators, || or OR?

I remember reading a while back in regards to logical operators that in the case of OR, using || was better than or (or vice versa).

I just had to use this in my project when it came back to me, but I can't remember which operator was recommended or if it was even true.

Which is better and why?

Upvotes: 123

Views: 180224

Answers (8)

janhsh
janhsh

Reputation: 96

Some languages use short-circuit, and others use full Boolean evaluation (if you know, this is similar to the directive $B in Pascal).

Explanations:

function A(){
    ...Do something..
    return true;
}

function B(){
    ...Do something..
    return true;
}

if ( A() OR B() ) { .....

In this example the function B() will never be executed. Since the function A() returns TRUE, the result of the OR statement is known from the first part without it being necessary to evaluate the second part of the expression.

However with ( A() || B() ), the second part is always evaluated regardless of the value of the first.

For optimized programming, you should always use OR which is faster (except for the case when the first part returns false and second part actually needs to be evaluated).

Upvotes: -4

improgrammer
improgrammer

Reputation: 582

Source: http://wallstreetdeveloper.com/php-logical-operators/

Here is sample code for working with logical operators:

<html>

<head>
    <title>Logical</title>
</head>

<body>
    <?php
        $a = 10;
        $b = 20;
        if ($a>$b)
        {
            echo " A is Greater";
        }
        elseif ($a<$b)
        {
            echo " A is lesser";
        }
        else
        {
             echo "A and B are equal";
        }
    ?>
    <?php
        $c = 30;
        $d = 40;
        //if (($a<$c) AND ($b<$d))
        if (($a<$c) && ($b<$d))
        {
            echo "A and B are larger";
        }
        if (isset($d))
            $d = 100;
        echo $d;
        unset($d);
    ?>
    <?php
        $var1 = 2;
        switch($var1)
        {
            case 1:  echo "var1 is 1";
                     break;
            case 2:  echo "var1 is 2";
                     break;
            case 3:  echo "var1 is 3";
                     break;
            default: echo "var1 is unknown";
        }
    ?>
</body>
</html>

Upvotes: 5

Zdeněk
Zdeněk

Reputation: 331

I know it's an old topic but still. I've just met the problem in the code I am debugging at work and maybe somebody may have similar issue...

Let's say the code looks like this:

$positions = $this->positions() || [];

You would expect (as you are used to from e.g. javascript) that when $this->positions() returns false or null, $positions is empty array. But it isn't. The value is TRUE or FALSE depends on what $this->positions() returns.

If you need to get value of $this->positions() or empty array, you have to use:

$positions = $this->positions() or [];

EDIT:

The above example doesn't work as intended but the truth is that || and or is not the same... Try this:

<?php

function returnEmpty()
{
  //return "string";
  //return [1];
  return null;
}

$first = returnEmpty() || [];
$second = returnEmpty() or [];
$third = returnEmpty() ?: [];

var_dump($first);
var_dump($second);
var_dump($third);
echo "\n";

This is the result:

bool(false)
NULL
array(0) {
}

So, actually the third option ?: is the correct solution when you want to set returned value or empty array.

$positions = $this->positions() ?: [];

Tested with PHP 7.2.1

Upvotes: 3

John Slegers
John Slegers

Reputation: 47111

The difference between respectively || and OR and && and AND is operator precedence :

$bool = FALSE || TRUE;

  • interpreted as ($bool = (FALSE || TRUE))
  • value of $bool is TRUE

$bool = FALSE OR TRUE;

  • interpreted as (($bool = FALSE) OR TRUE)
  • value of $bool is FALSE

$bool = TRUE && FALSE;

  • interpreted as ($bool = (TRUE && FALSE))
  • value of $bool is FALSE

$bool = TRUE AND FALSE;

  • interpreted as (($bool = TRUE) AND FALSE)
  • value of $bool is TRUE

Upvotes: 41

Nishu Tayal
Nishu Tayal

Reputation: 20880

There is nothing bad or better, It just depends on the precedence of operators. Since || has higher precedence than or, so || is mostly used.

Upvotes: 0

user752897
user752897

Reputation:

I don't think one is inherently better than another one, but I would suggest sticking with || because it is the default in most languages.

EDIT: As others have pointed out there is indeed a difference between the two.

Upvotes: 0

Felix Kling
Felix Kling

Reputation: 817030

There is no "better" but the more common one is ||. They have different precedence and || would work like one would expect normally.

See also: Logical operators (the following example is taken from there):

// The result of the expression (false || true) is assigned to $e
// Acts like: ($e = (false || true))
$e = false || true;

// The constant false is assigned to $f and then true is ignored
// Acts like: (($f = false) or true)
$f = false or true;

Upvotes: 167

Matthew Ratzloff
Matthew Ratzloff

Reputation: 4623

They are used for different purposes and in fact have different operator precedences. The && and || operators are intended for Boolean conditions, whereas and and or are intended for control flow.

For example, the following is a Boolean condition:

if ($foo == $bar && $baz != $quxx) {

This differs from control flow:

doSomething() or die();

Upvotes: 55

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