language/control-structures/switch.xml
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<!-- $Revision$ -->
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<sect1 xml:id="control-structures.switch" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
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<title><literal>switch</literal></title>
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<title>switch</title>
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<?phpdoc print-version-for="switch"?>
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<simpara>
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The <literal>switch</literal> statement is similar to a series of
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<simpara>
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Note that unlike some other languages, the
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<link linkend="control-structures.continue">continue</link> statement
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applies to switch and acts similar to <literal>break</literal>. If you
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have a switch inside a loop and wish to continue to the next iteration of
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applies to <literal>switch</literal> and acts similar to <literal>break</literal>. If you
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have a <literal>switch</literal> inside a loop and wish to continue to the next iteration of
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the outer loop, use <literal>continue 2</literal>.
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</simpara>
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</note>
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<link linkend="types.comparisions-loose">loose comparison</link>.
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</para>
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</note>
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<para>
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<table>
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&reftitle.changelog;
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<tgroup cols="2">
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<thead>
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<row>
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<entry>&Version;</entry>
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<entry>&Description;</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>7.0.0</entry>
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<entry>
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Multiple default cases will raise a <constant>E_COMPILE_ERROR</constant> error.
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</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</para>
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<para>
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The following two examples are two different ways to write the
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same thing, one using a series of <literal>if</literal> and
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<literal>elseif</literal> statements, and the other using the
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<literal>switch</literal> statement:
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In the following example, each code block is equivalent.
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One uses a series of <literal>if</literal> and
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<literal>elseif</literal> statements, and the other a
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<literal>switch</literal> statement. In each case, the output is the same.
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<example>
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<title><literal>switch</literal> structure</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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if ($i == 0) {
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echo "i equals 0";
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} elseif ($i == 1) {
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echo "i equals 1";
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} elseif ($i == 2) {
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echo "i equals 2";
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}
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// This switch statement:
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switch ($i) {
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case 0:
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echo "i equals 2";
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break;
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}
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?>
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]]>
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</programlisting>
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</example>
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<example>
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<title><literal>switch</literal> structure allows usage of strings</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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switch ($i) {
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case "apple":
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echo "i is apple";
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break;
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case "bar":
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echo "i is bar";
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break;
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case "cake":
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echo "i is cake";
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break;
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// Is equivalent to:
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if ($i == 0) {
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echo "i equals 0";
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} elseif ($i == 1) {
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echo "i equals 1";
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} elseif ($i == 2) {
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echo "i equals 2";
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}
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?>
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]]>
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<literal>switch</literal> statement executes line by line
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(actually, statement by statement). In the beginning, no code is
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executed. Only when a <literal>case</literal> statement is found
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with a value that matches the value of the
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whose expression evaluates to a value that matches the value of the
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<literal>switch</literal> expression does PHP begin to execute the
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statements. PHP continues to execute the statements until the end
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of the <literal>switch</literal> block, or the first time it sees
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<![CDATA[
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<?php
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switch ($i) {
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case 0:
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case 1:
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case 2:
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echo "i is less than 3 but not negative";
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break;
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case 3:
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echo "i is 3";
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case 0:
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case 1:
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case 2:
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echo "i is less than 3 but not negative";
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break;
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case 3:
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echo "i is 3";
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}
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?>
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]]>
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]]>
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</programlisting>
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</informalexample>
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<note>
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<simpara>
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Multiple default cases will raise a
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<constant>E_COMPILE_ERROR</constant> error.
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</simpara>
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</note>
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<note>
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<simpara>
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Technically the <literal>default</literal> case may be listed
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in any order. It will only be used if no other case matches.
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However, by convention it is best to place it at the end as the
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last branch.
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</simpara>
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</note>
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</para>
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<para>
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If no <literal>case</literal> branch matches, and there is no <literal>default</literal>
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branch, then no code will be executed, just as if no <literal>if</literal> statement was true.
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</para>
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<para>
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A case value may be given as an expression. However, that expression will be
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evaluated on its own and then loosely compared with the switch value. That means
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it cannot be used for complex evaluations of the switch value. For example:
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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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$target = 1;
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$start = 3;
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switch ($target) {
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case $start - 1:
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print "A";
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break;
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case $start - 2:
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print "B";
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break;
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case $start - 3:
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print "C";
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break;
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case $start - 4:
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print "D";
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break;
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}
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// Prints "B"
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?>
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]]>
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</programlisting>
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</informalexample>
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</para>
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<para>
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The <literal>case</literal> expression may be any expression that
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evaluates to a simple type, that is, integer or floating-point
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numbers and strings. Arrays or objects cannot be used here unless
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they are dereferenced to a simple type.
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For more complex comparisons, the value &true; may be used as the switch value.
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Or, alternatively, <literal>if</literal>-<literal>else</literal> blocks instead of <literal>switch</literal>.
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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<?php
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$offset = 1;
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$start = 3;
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switch (true) {
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case $start - $offset === 1:
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print "A";
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break;
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case $start - $offset === 2:
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print "B";
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break;
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case $start - $offset === 3:
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print "C";
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break;
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case $start - $offset === 4:
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print "D";
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break;
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}
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// Prints "B"
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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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<para>
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The alternative syntax for control structures is supported with
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{
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case 'tuborg';
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case 'carlsberg';
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case 'stella';
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case 'heineken';
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echo 'Good choice';
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break;
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break;
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default;
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echo 'Please make a new selection...';
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break;
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break;
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}
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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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<sect2 role="seealso">
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&reftitle.seealso;
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<para>
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<simplelist>
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<member>&match;</member>
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</simplelist>
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</para>
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</sect2>
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</sect1>
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<!-- Keep this comment at the end of the file
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