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<?xml version="1.0" encoding="utf-8"?>
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<sect1 xml:id="control-structures.if" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
<title>if</title>
<?phpdoc print-version-for="if"?>
<para>
The <literal>if</literal> construct is one of the most important
features of many languages, PHP included. It allows for
conditional execution of code fragments. PHP features an
<literal>if</literal> structure that is similar to that of C:
<informalexample>
<programlisting>
<![CDATA[
if (expr)
statement
]]>
</programlisting>
</informalexample>
</para>
<simpara>
As described in <link linkend="language.expressions">the section about
expressions</link>, <replaceable>expression</replaceable> is evaluated to its
Boolean value. If <replaceable>expression</replaceable> evaluates to &true;,
PHP will execute <replaceable>statement</replaceable>, and if it evaluates
to &false; - it'll ignore it. More information about what values evaluate
to &false; can be found in the <link
linkend="language.types.boolean.casting">'Converting to boolean'</link>
section.
</simpara>
<para>
The following example would display <computeroutput>a is bigger
than b</computeroutput> if <varname>$a</varname> is bigger
than <varname>$b</varname>:
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
if ($a > $b)
echo "a is bigger than b";
?>
]]>
</programlisting>
</informalexample>
</para>
<para>
Often you'd want to have more than one statement to be executed
conditionally. Of course, there's no need to wrap each statement
with an <literal>if</literal> clause. Instead, you can group
several statements into a statement group. For example, this code
would display <computeroutput>a is bigger than b</computeroutput>
if <varname>$a</varname> is bigger than
<varname>$b</varname>, and would then assign the value of
<varname>$a</varname> into <varname>$b</varname>:
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
if ($a > $b) {
echo "a is bigger than b";
$b = $a;
}
?>
]]>
</programlisting>
</informalexample>
</para>
<simpara>
<literal>If</literal> statements can be nested infinitely within other
<literal>if</literal> statements, which provides you with complete
flexibility for conditional execution of the various parts of your
program.
</simpara>
</sect1>
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