Introdução
As an added note to the guy below, in such a case, use the !== operator like this.
$nkey = array_search($needle, $haystack);
if ($nkey !== false) { ...
The !== and the === compare the "types". So, with this type of comparision, 0 is not the same as the FALSE returned by the array_search array when it can not find a match. :)
Quoted Text:
===================================
Be careful with stuff like
if ($nkey = array_search($needle, $haystack)) { ...
if the returned key is actually the key 0, then the if won't be executed
===================================
if
The if construct is one of the most important features of many languages, PHP included. It allows for conditional execution of code fragments. PHP features an if structure that is similar to that of C:
if (expr) statement
As described in the section about expressions, expression is evaluated to its Boolean value. If expression evaluates to TRUE, PHP will execute statement, and if it evaluates to FALSE - it'll ignore it. More information about what values evaluate to FALSE can be found in the 'Converting to boolean' section.
The following example would display a is bigger than b if $a is bigger than $b:
<?php
if ($a > $b)
echo "a is bigger than b";
?>
Often you'd want to have more than one statement to be executed conditionally. Of course, there's no need to wrap each statement with an if clause. Instead, you can group several statements into a statement group. For example, this code would display a is bigger than b if $a is bigger than $b, and would then assign the value of $a into $b:
<?php
if ($a > $b) {
echo "a is bigger than b";
$b = $a;
}
?>
If statements can be nested infinitely within other if statements, which provides you with complete flexibility for conditional execution of the various parts of your program.
add a note
User Contributed Notesif
austinderrick2 at gmail dot com
03-Oct-2009 11:50
03-Oct-2009 11:50
jm+phpweb at roth dot lu
28-Aug-2009 09:25
28-Aug-2009 09:25
Be careful with stuff like
if ($nkey = array_search($needle, $haystack)) { ...
if the returned key is actually the key 0, then the if won't be executed
php dot net at bgr8 dot com
24-Aug-2009 04:17
24-Aug-2009 04:17
an interesting concept, using only double == ... but i'm executing php from the command line on an ubuntu server using php5 ... and if i use ==, the function fails, but if i use = the function works.
i try it with good and bad value pairs echoing "match" to the screen when they match (the executed line) and "match" will not happen with ==. only with =. neither one tosses an error, but the == NEVER shows a match and the = matches when the two strings being compared actually match. this is not something i was expecting after programming in several languages.
go figure.
#!/usr/bin/php
<?php
if ($check = $output)
echo "match\n";
?>
obviously there's code to make them match or not match, but that code does not change. i JUST add/remove an = and the code works with =.
strata_ranger at hotmail dot com
05-Apr-2009 01:13
05-Apr-2009 01:13
Although most programmers are aware of this already, if for whatever reason you need to 'break' out of an if() block (which, unlike switch() is not considered a looping structure) just wrap it in an appropriate looping structure, such as a do-while(false):
<?php
do if ($foo)
{
// Do something first...
// Shall we continue with this block, or exit now?
if ($abort_if_block) break;
// Continue doing something...
} while (false);
?>
Anonymous
02-Apr-2009 12:32
02-Apr-2009 12:32
If you need to do something when a function return FALSE and nothing when it return TRUE you can do it like that :
<?php
function call()
{
return FALSE;
}
if(call()==TRUE) // or if(call())
{
// nothing to do
}
else
{
// do something here
}
?>
You can also write it like this :
<?php
if(!call()==TRUE) // or if(!call())
{
// do something here
}
// here '!' will invert 'FALSE' (from call()) into 'TRUE'
?>
/!\ WARNING /!\
The '!' only work with booleans !
Check http://fr.php.net/manual/en/language.types.boolean.php to know if you can use '!'
If you want to compare two strings and use '!' be careful how you use it !!!!
<?php
$string1 = "cake";
$string2 = "foo";
if(!$string1==$string2)
{
echo "cake is a lie";
}
//this will ALWAYS fail without exception because '!' is applied to $string1 and not to '$string1==$string2'
//to work, you have to do like this
if(!($string1==$string2))
{
echo "cake is a lie";
}
//it will display 'cake is a lie' because ($string1==$string2) return FALSE and '!' will invert it into TRUE
?>
For array/float, it's the same !
contact at bsorin dot romania
07-Mar-2009 04:28
07-Mar-2009 04:28
This has got the better part of my last 2 hours, so I'm putting it here, maybe it will save someone some time.
I had a
if (function1() && function2())
statement. Before returning true or false, function1() and function2() had to output some text. The trick is that, if function1() returns false, function2() is not called at all. It seems I should have known that, but it slipped my mind.
Anonymous
28-Sep-2008 12:03
28-Sep-2008 12:03
Re : henryk dot kwak at gmail dot com
<?php function message($m)
{
echo "$m <br />\r";
return true;
}
$k=false;
if (message("first")&& $k && message("second")){;}
// will show
//first
class
$k=true;
if (message("first")&& $k && message("second")){;}
// will show
//first
//second
?>
john
25-Sep-2008 03:24
25-Sep-2008 03:24
@henryk (and everybody):
You should put your arguments in order by *least* likely to be true. That way if php is going to be able to quit checking, it will happen sooner rather than later, and your script will run (what amounts to unnoticeably) faster.
At least, that makes the most sense to me, but I don't claim omniscience.
Wiseguy
28-Aug-2008 02:22
28-Aug-2008 02:22
RE: chrislabricole at yahoo dot fr on 09-Aug-2008 05:53
You're referring to the ternary operator.
http://php.net/manual/en/language.operators.comparison.php
jchau at bu dot edu
14-Aug-2008 05:50
14-Aug-2008 05:50
RE: henryk dot kwak at gmail dot com's comment from 04-May-2008 05:01
I think you made a mistake.
For maximum efficiency, assuming each expression requires the same amount of processing, the expression that is least likely to be true should come first for expressions connected by && (and). This will reduce the probability that later expressions will need to be evaluated.
The opposite is true for || (or). If the most likely expression comes first, then the probability of needing to evaluate later expressions is reduced.
chrislabricole at yahoo dot fr
10-Aug-2008 12:53
10-Aug-2008 12:53
You can do IF with this pattern :
<?php
$var = TRUE;
echo $var==TRUE ? 'TRUE' : 'FALSE'; // get TRUE
echo $var==FALSE ? 'TRUE' : 'FALSE'; // get FALSE
?>
henryk dot kwak at gmail dot com
05-May-2008 12:01
05-May-2008 12:01
When you use if command with many condidions like
if ( expr1 && expr2 && expr3 && etc. )
it is more effective to put expressions in special order
Firstly you should put that, which has the biggest
probability to occur.
This is because PHP checks each condition in order from left to right and it takes some time to check each condition.
grawity at gmail dot com
10-Mar-2008 11:41
10-Mar-2008 11:41
re: #80305
Again useful for newbies:
if you need to compare a variable with a value, instead of doing
<?php
if ($foo == 3) bar();
?>
do
<?php
if (3 == $foo) bar();
?>
this way, if you forget a =, it will become
<?php
if (3 = $foo) bar();
?>
and PHP will report an error.
redrobinuk at aol dot com
09-Jan-2008 10:54
09-Jan-2008 10:54
This is aimed at PHP beginners but many of us do this Ocasionally...
When writing an if statement that compares two values, remember not to use a single = statement.
eg:
<?php
if ($a = $b)
{
print("something");
}
?>
This will assign $a the value $b and output the statement.
To see if $a is exactly equal to $b (value not type) It should be:
<?php
if ($a == $b)
{
print("something");
}
?>
Simple stuff but it can cause havok deep in classes/functions etc...