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https://github.com/sigmasternchen/php-doc-en
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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@312947 c90b9560-bf6c-de11-be94-00142212c4b1
101 lines
2.9 KiB
XML
101 lines
2.9 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<sect1 xml:id="control-structures.do.while" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
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<title><literal>do-while</literal></title>
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<?phpdoc print-version-for="dowhile"?>
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<simpara>
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<literal>do-while</literal> loops are very similar to
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<literal>while</literal> loops, except the truth expression is
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checked at the end of each iteration instead of in the beginning.
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The main difference from regular <literal>while</literal> loops is
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that the first iteration of a <literal>do-while</literal> loop is
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guaranteed to run (the truth expression is only checked at the end
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of the iteration), whereas it may not necessarily run with a
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regular <literal>while</literal> loop (the truth expression is
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checked at the beginning of each iteration, if it evaluates to
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&false; right from the beginning, the loop
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execution would end immediately).
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</simpara>
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<para>
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There is just one syntax for <literal>do-while</literal> loops:
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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<?php
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$i = 0;
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do {
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echo $i;
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} while ($i > 0);
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?>
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]]>
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</programlisting>
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</informalexample>
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</para>
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<simpara>
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The above loop would run one time exactly, since after the first
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iteration, when truth expression is checked, it evaluates to
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&false; (<varname>$i</varname> is not bigger than 0) and the loop
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execution ends.
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</simpara>
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<para>
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Advanced C users may be familiar with a different usage of the
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<literal>do-while</literal> loop, to allow stopping execution in
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the middle of code blocks, by encapsulating them with
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<literal>do-while</literal> (0), and using the <link
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linkend="control-structures.break"><literal>break</literal></link>
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statement. The following code fragment demonstrates this:
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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<?php
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do {
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if ($i < 5) {
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echo "i is not big enough";
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break;
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}
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$i *= $factor;
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if ($i < $minimum_limit) {
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break;
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}
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echo "i is ok";
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/* process i */
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} while (0);
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?>
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]]>
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</programlisting>
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</informalexample>
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</para>
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<simpara>
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Don't worry if you don't understand this right away or at all.
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You can code scripts and even powerful scripts without using this
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'feature'.
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Since PHP 5.3.0, it is possible to use
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<link linkend="control-structures.goto"><literal>goto</literal></link>
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operator instead of this hack.
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</simpara>
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</sect1>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"~/.phpdoc/manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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