File: if.xml

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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->

<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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