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does the condition after && always get evaluated

Posted by: admin November 30, 2017 Leave a comment

Questions:

I have this if statement that tests for the 2 conditions below. The second one is a function goodToGo() so I want to call it unless the first condition is already true

$value = 2239;

if ($value < 2000 && goodToGo($value)){
   //do stuff
}

function goodToGo($value){
   $ret = //some processing of the value
   return $ret; 
}

My question is about the 2 if conditions $value < 2000 && goodToGo($value). Do they both get evaluated or does the second one only get evaluated when the first one is true?

In other words, are the following 2 blocks the same?

if($value < 2000 && goodToGo($value)) {
   //stuff to do
}

if($value < 2000) {
    if (goodToGo($value)){
       //stuff to do
    }
}
Answers:

No–the second condition won’t always be executed (which makes your examples equivalent).

PHP’s &&, ||, and, and or operators are implemented as “short-circuit” operators. As soon as a condition is found that forces the result for the overall conditional, evaluation of subsequent conditions stops.

From http://www.php.net/manual/en/language.operators.logical.php

// --------------------
// foo() will never get called as those operators are short-circuit

$a = (false && foo());
$b = (true  || foo());
$c = (false and foo());
$d = (true  or  foo());

Questions:
Answers:

Yes. The two blocks are the same. PHP, like most (but not all) languages, uses short-circuit evaluation for && and ||.

Questions:
Answers:

The two blocks ARE same.

PHP logical operators are “lazy”, they are evaluated only if they are needed.
The following code prints “Hello, world!”:

<?php
$a = 10;
isset($a) || die ("variable $a does not exist.");
print "Hello, world!"
?>

Other logical operators includes &&, and, or.

<?php
perform_action() or die ('failed to perform the action');
?>

is a popular idiom.

Questions:
Answers:

the second condition will only be checked if and only if first one is true, hence both statements are equivalent.

Questions:
Answers:

Yes, the 2 code blocks you gave are equivalent. PHP has short-circuiting, so when you use
|| and &&, any statement after the first only gets evaluated when necessary.

Questions:
Answers:

Always corelate your technical Language with your own language, Likewise here, If I say you in verbal conversation, its just like :You are asking= “if I am hungry ‘&&’ I am eating Pizza” is similar to “If I am hungry then only i am eating Pizza”?
So here you can see that later phrase says that untill i am not hungry i am not eating pizza, and the former says I am humgry and I am eating pizza.
🙂

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