PHP Conference Japan 2024

if

(PHP 4, PHP 5, PHP 7, PHP 8)

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.

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User Contributed Notes 5 notes

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178
robk
11 years ago
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 ?>
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2
georgy dot moshkin at techsponsor dot io
4 months ago
Left-to-right evaluation of && operators has one useful feature: evaluation stops after first "false" operand is encountered.

This feature can be useful for creating following construction:

$someVar==123 is not evaluated, so there will be no warnings such as "Undefined variable $someVar":
<?php
// $someVar=123; - commented line
if ((!empty($someVar))&&($someVar==123))
{
echo
$someVar;
}
?>

Function someFunc($someVar) will not be called:
<?php
// $someVar=123; - commented line
if ((!empty($someVar))&&(someFunc($someVar)))
{
echo
$someVar;
}
?>

This will give "Warning: Undefined variable $someVar" error. Order matters:
<?php
// $someVar=123;
if ((someFunc($someVar))&&(!empty($someVar)))
{
echo
$someVar;
}
?>
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44
techguy14 at gmail dot com
13 years ago
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!
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22
grawity at gmail dot com
16 years ago
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.
up
16
Christian L.
13 years ago
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.
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