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<h3 class="section">10.2 The switch Statement</h3>
<p><a name="index-g_t_0040code_007bswitch_007d-statement-694"></a><a name="index-g_t_0040code_007bcase_007d-statement-695"></a><a name="index-g_t_0040code_007botherwise_007d-statement-696"></a><a name="index-g_t_0040code_007bendswitch_007d-statement-697"></a>
It is very common to take different actions depending on the value of
one variable. This is possible using the <code>if</code> statement in the
following way
<pre class="example"> if (X == 1)
do_something ();
elseif (X == 2)
do_something_else ();
else
do_something_completely_different ();
endif
</pre>
<p class="noindent">This kind of code can however be very cumbersome to both write and
maintain. To overcome this problem Octave supports the <code>switch</code>
statement. Using this statement, the above example becomes
<pre class="example"> switch (X)
case 1
do_something ();
case 2
do_something_else ();
otherwise
do_something_completely_different ();
endswitch
</pre>
<p class="noindent">This code makes the repetitive structure of the problem more explicit,
making the code easier to read, and hence maintain. Also, if the
variable <code>X</code> should change its name, only one line would need
changing compared to one line per case when <code>if</code> statements are
used.
<p>The general form of the <code>switch</code> statement is
<pre class="example"> switch <var>expression</var>
case <var>label</var>
<var>command_list</var>
case <var>label</var>
<var>command_list</var>
...
otherwise
<var>command_list</var>
endswitch
</pre>
<p class="noindent">where <var>label</var> can be any expression. However, duplicate
<var>label</var> values are not detected, and only the <var>command_list</var>
corresponding to the first match will be executed. For the
<code>switch</code> statement to be meaningful at least one
<code>case </code><var>label</var> <var>command_list</var> clause must be present,
while the <code>otherwise </code><var>command_list</var> clause is optional.
<p>If <var>label</var> is a cell array the corresponding <var>command_list</var>
is executed if <em>any</em> of the elements of the cell array match
<var>expression</var>. As an example, the following program will print
‘<samp><span class="samp">Variable is either 6 or 7</span></samp>’.
<pre class="example"> A = 7;
switch A
case { 6, 7 }
printf ("variable is either 6 or 7\n");
otherwise
printf ("variable is neither 6 nor 7\n");
endswitch
</pre>
<p>As with all other specific <code>end</code> keywords, <code>endswitch</code> may be
replaced by <code>end</code>, but you can get better diagnostics if you use
the specific forms.
<!-- Strings can be matched -->
<p>One advantage of using the <code>switch</code> statement compared to using
<code>if</code> statements is that the <var>label</var>s can be strings. If an
<code>if</code> statement is used it is <em>not</em> possible to write
<pre class="example"> if (X == "a string") # This is NOT valid
</pre>
<p class="noindent">since a character-to-character comparison between <code>X</code> and the
string will be made instead of evaluating if the strings are equal.
This special-case is handled by the <code>switch</code> statement, and it
is possible to write programs that look like this
<pre class="example"> switch (X)
case "a string"
do_something
...
endswitch
</pre>
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