if

(PHP 4, PHP5)

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 , 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 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.

User Contributed Notes

bimal at sanjaal dot com
PHP compares numbers inside quotations, in an interesting way.
This can create confusions to those who did not refer this manual, but expected something different.

<?php

define('NUMBER', 13);
$number = NUMBER;

if('13_2' == NUMBER) { echo('Why matched?'); };
if('13_2' == "{$number}") { echo('Why not matched?'); }

?>

In the above example, the first comparison matches; that you don't expect.

The second comparison does not match.
lallemand dot mathieu at gmail dot com
Be careful when you chain inline "if" :

<?php
$x = 1;
$y = 3;
echo ($x==1) ? "One" : ($y == 2) ? "Two" : "None";
?>

Expected result : "One".
Result on screen : "Two".

Pretty disapointing isn't it ?

So, if you want to chain inline "if" you have to use parentesis on each test like below:

<?php
$x=1;
$y=3;
echo ($x==1) ? "One" : ( ($y==2) ? "Two" : "None" );
?>

Result on screen : "One".

Hope it helps !
Donny Nyamweya
In addition to the traditional syntax for if (condition) action;
I am fond of the ternary operator that does the same thing, but with fewer words and code to type:

(condition ? action_if_true: action_if_false;)

example

(x > y? 'Passed the test' : 'Failed the test')
Christian L.
An other way for controls is the ternary operator (see Comparison Operators) that can be used as follows:

<?php
$v = 1;

$r = (1 == $v) ? 'Yes' : 'No'; // $r is set to 'Yes'
$r = (3 == $v) ? 'Yes' : 'No'; // $r is set to 'No'

echo (1 == $v) ? 'Yes' : 'No'; // 'Yes' will be printed

// and since PHP 5.3
$v = 'My Value';
$r = ($v) ?: 'No Value'; // $r is set to 'My Value' because $v is evaluated to TRUE

$v = '';
echo ($v) ?: 'No Value'; // 'No Value' will be printed because $v is evaluated to FALSE
?>

Parentheses can be left out in all examples above.
techguy14 at gmail dot com
You can have 'nested' if statements withing a single if statement, using additional parenthesis.
For example, instead of having:

<?php
if( $a == 1 || $a == 2 ) {
    if( $b == 3 || $b == 4 ) {
        if( $c == 5 || $ d == 6 ) {
             //Do something here.
        }
    }
}
?>

You could just simply do this:

<?php
if( ($a==1 || $a==2) && ($b==3 || $b==4) && ($c==5 || $c==6) ) {
    //do that something here.
}
?>

Hope this helps!
admin at leonard !spam challis dot com
When using if statements without the curly braces, remember than only one statement will be executed as part of that condition. If you want to place multiple statements you must use curly braces, and not just put them on the same line.

<?php

if (1==0) echo "Test 1."; echo "Test 2";

?>

Whereas some people would expect nothing to be displayed, this piece of code will show: "Test 2".
Rudi
Note that safe type checking (using === and !== instead of == and !=) is in general somewhat faster. When you're using non-safe type checking and a conversion is really needed for checking, safe type checking is considerably faster.

===================================
Test (100,000,000 runs):
<?php
$start = microtime(true);
for($i = 0; $i < 100000000; $i++)
    if(5 == 10) {}
$end = microtime(true);
echo "1: ".($end - $start)."<br />\n";
unset($start, $end);

$start = microtime(true);
for($i = 0; $i < 100000000; $i++)
    if('foobar' == 10) {}
$end = microtime(true);
echo "2: ".($end - $start)."<br />\n";
unset($start, $end);

$start = microtime(true);
for($i = 0; $i < 100000000; $i++)
    if(5 === 10) {}
$end = microtime(true);
echo "3: ".($end - $start)."<br />\n";
unset($start, $end);

$start = microtime(true);
for($i = 0; $i < 100000000; $i++)
    if('foobar' === 10) {}
$end = microtime(true);
echo "4: ".($end - $start)."<br />\n";
unset($start, $end);
?>

===================================
Result (depending on hardware configuration):
1: 16.779544115067
2: 21.305675029755
3: 16.345532178879
4: 15.991420030594
austinderrick2 at gmail dot com
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
===================================
jm+phpweb at roth dot lu
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
strata_ranger at hotmail dot com
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
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 '!'

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
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
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
@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
RE: chrislabricole at yahoo dot fr on 09-Aug-2008 05:53

You're referring to the ternary operator.

jchau at bu dot edu
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
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
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
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
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...