Chapter 16. Control Structures

Table of Contents
if
else
elseif
Alternative syntax for control structures
while
do-while
for
foreach
break
continue
switch
declare
return
require()
include()
require_once()
include_once()

Any PHP script is built out of a series of statements. A statement can be an assignment, a function call, a loop, a conditional statement of even a statement that does nothing (an empty statement). Statements usually end with a semicolon. In addition, statements can be grouped into a statement-group by encapsulating a group of statements with curly braces. A statement-group is a statement by itself as well. The various statement types are described in this chapter.

`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:

<?php
if (expression)
    statement
?>

As described in the section about expressions, expr is evaluated to its Boolean value. If expr 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.

User Contributed Notes
Control Structures

macristo[AT]gmx[DOT]net
06-May-2005 02:01


It is not mandatory to use the parentheses in an if-statement.

This is an if-statement on one line and it's perfectly valid code:



<?php

$a = "foo";

if ("foo" == $a) echo "bar";

?>



will output:

"bar"

dotwho at nospam dot mac dot com
17-Feb-2005 07:12


As of php 5.01:



if using the short cut if - else syntax:



condition ? true : false;



be careful. inside of condition the and / or operators do not work as expected. use instead && / ||.



Example:

<?php

$sText = (!isset($searchText) or $sText === "" ?  "NULL" : $sText);

?>

Always sets $sText to "1".



<?php

$sText = (!isset($searchText) || $sText === "" ?  "NULL" : $sText);

?>

Sets $sText appropriately.

niels dot laukens at tijd dot com
26-Dec-2004 09:49


For the people that know C: php is lazy when evaluating expressions. That is, as soon as it knows the outcome, it'll stop processing.



<?php

if ( FALSE && some_function() )

    echo "something";

// some_function() will not be called, since php knows that it will never have to execute the if-block

?>



This comes in nice in situations like this:

<?php

if ( file_exists($filename) && filemtime($filename) > time() )

    do_something();

// filemtime will never give an file-not-found-error, since php will stop parsing as soon as file_exists returns FALSE

?>

Job Oberio
21-Oct-2004 03:19


if you want to have two expressions you can

use any logical operators  'and', 'or'



<?php

if ($num > 10 and $num < 15)

       {

            echo "number is greater than 10 but less than 15";         

       }

?> 



another way, you can enclose each expression into 

open/close parentheses - ( expression1 ) and (expression2)

so that its easy to analyze your expressions



<?php

if ( ($num > 10) and ($num < 15) )

       {

            echo "number is greater than 10 but less than 15";         

       }

?> 



i prefer using the wordings 'and' instead of '&&' operator

because wordings operators are easy to analyze and easy 

to your eye to read especially for long expressions.

the '&&' tends to be confused to $ sign