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 indefinitely within other if statements, which provides you with complete flexibility for conditional execution of the various parts of your program.

Коментарии

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...
2008-01-09 04:54:05
http://php5.kiev.ua/manual/ru/control-structures.if.html
re: #80305

Again useful for newbies:

if you need to compare a variable with a value, instead of doing

<?php
if ($foo == 3bar();
?>

do

<?php
if (== $foobar();
?>

this way, if you forget a =, it will become

<?php
if ($foobar();
?>

and PHP will report an error.
2008-03-10 05:41:06
http://php5.kiev.ua/manual/ru/control-structures.if.html
You can do IF with this pattern :
<?php
$var 
TRUE;
echo 
$var==TRUE 'TRUE' 'FALSE'// get TRUE
echo $var==FALSE 'TRUE' 'FALSE'// get FALSE
?>
2008-08-09 20:53:51
http://php5.kiev.ua/manual/ru/control-structures.if.html
Автор:
@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.
2008-09-24 23:24:59
http://php5.kiev.ua/manual/ru/control-structures.if.html
Автор:
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 
?>
2008-09-28 08:03:35
http://php5.kiev.ua/manual/ru/control-structures.if.html
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.
2009-03-07 10:28:14
http://php5.kiev.ua/manual/ru/control-structures.if.html
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
===================================
2009-10-03 07:50:02
http://php5.kiev.ua/manual/ru/control-structures.if.html
Автор:
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(
== 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(
=== 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
2010-09-14 16:14:09
http://php5.kiev.ua/manual/ru/control-structures.if.html
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".
2010-11-22 06:41:01
http://php5.kiev.ua/manual/ru/control-structures.if.html
You can have 'nested' if statements withing a single if statement, using additional parenthesis.
For example, instead of having:

<?php
if( $a == || $a == ) {
    if( 
$b == || $b == ) {
        if( 
$c == || $ == ) {
             
//Do something here.
       
}
    }
}
?>

You could just simply do this:

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

Hope this helps!
2011-01-06 15:39:11
http://php5.kiev.ua/manual/ru/control-structures.if.html
Автор:
An other way for controls is the ternary operator (see Comparison Operators) that can be used as follows:

<?php
$v 
1;

$r = (== $v) ? 'Yes' 'No'// $r is set to 'Yes'
$r = (== $v) ? 'Yes' 'No'// $r is set to 'No'

echo (== $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.
2011-01-25 12:58:14
http://php5.kiev.ua/manual/ru/control-structures.if.html
Автор:
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')
2011-02-11 22:30:25
http://php5.kiev.ua/manual/ru/control-structures.if.html
It seems that only numbers can be compared between them but actually an alphabet can be compare too. For example :

<?php
 
// Number comparison
 
$a="C";
 
$b="X";
  if (
$a<$b)
     {
    echo 
$a."is smaller than".$b;
    }               
// Result : C is smaller than X
?>
2012-02-28 11:31:33
http://php5.kiev.ua/manual/ru/control-structures.if.html
Автор:
easy way to execute conditional html / javascript / css / other language code with php if else:

<?php if (condition): ?>

html code to run if condition is true

<?php else: ?>

html code to run if condition is false

<?php endif ?>
2013-05-20 04:02:05
http://php5.kiev.ua/manual/ru/control-structures.if.html
You can also check alphabet characters like this

<?php
// Alphabetical Comparison
 
$a="brian";
 
$b="zebra";
      if (
$a $b){
        echo 
$a." is before ".$b." in the alphabet";
      }
      else{
          echo 
$a." is after ".$b." in the alphabet";
      }
// Result : brian is before zebra in the alphabet
?>
2015-06-04 13:25:57
http://php5.kiev.ua/manual/ru/control-structures.if.html
Any variables defined inside the if block will be available outside the block. Remember that the if doesn't have its own scope.

<?php
$bool 
true;
if (
$bool) {
   
$hi 'Hello to all people!';
}
echo 
$hi;
?>

It will print 'Hello to all people!'

On the other hand, this will have no output:

<?php
if (false) {
   
$hi 'Hello to all people!';
}
echo 
$hi;
?>
2017-05-31 20:41:57
http://php5.kiev.ua/manual/ru/control-structures.if.html
'IF' STATEMENT WRONG BEHAVIOR 
If assign var to function that returns 0 as integer or 0 as string 'if' statement condition works as false. 

Test script:
---------------
//In this script you can see, that set var value to 0 is equal to boolean false 
//applied to if statement. There is no diff between integer 0 or string '0'

if($pos = 0){
    $pos++;
} else {
    $pos = 0;
}
var_dump($pos);

//$pos is not boolean false, so it should do if condition true, but it's not

//to make this work well i use this
$pos = 0;
if($pos !== false){
    $pos++;
} else {
    $pos = 0;
}
var_dump($pos);
2017-07-07 02:55:49
http://php5.kiev.ua/manual/ru/control-structures.if.html
$x = 1;
$y = 2;
if ($x != $y) 
  $x = $x * $y;
else 
  $x = $x + $y;

//can you guess the answer?
echo $x; #2
2018-08-08 11:14:44
http://php5.kiev.ua/manual/ru/control-structures.if.html

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