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<h3 class="section" id="The-switch-Statement-1"><span>10.2 The switch Statement<a class="copiable-link" href="#The-switch-Statement-1"> ¶</a></span></h3>
<a class="index-entry-id" id="index-switch-statement"></a>
<a class="index-entry-id" id="index-case-statement"></a>
<a class="index-entry-id" id="index-otherwise-statement"></a>
<a class="index-entry-id" id="index-endswitch-statement"></a>
<p>It is very common to take different actions depending on the value of
one variable. This is possible using the <code class="code">if</code> statement in the
following way
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">if (X == 1)
do_something ();
elseif (X == 2)
do_something_else ();
else
do_something_completely_different ();
endif
</pre></div></div>
<p>This kind of code can however be very cumbersome to both write and
maintain. To overcome this problem Octave supports the <code class="code">switch</code>
statement. Using this statement, the above example becomes
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">switch (X)
case 1
do_something ();
case 2
do_something_else ();
otherwise
do_something_completely_different ();
endswitch
</pre></div></div>
<p>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 class="code">X</code> should change its name, only one line would need
changing compared to one line per case when <code class="code">if</code> statements are
used.
</p>
<p>The general form of the <code class="code">switch</code> statement is
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">switch (<var class="var">expression</var>)
case <var class="var">label</var>
<var class="var">command_list</var>
case <var class="var">label</var>
<var class="var">command_list</var>
...
otherwise
<var class="var">command_list</var>
endswitch
</pre></div></div>
<p>where <var class="var">label</var> can be any expression. However, duplicate
<var class="var">label</var> values are not detected, and only the <var class="var">command_list</var>
corresponding to the first match will be executed. For the
<code class="code">switch</code> statement to be meaningful at least one
<code class="code">case <var class="var">label</var> <var class="var">command_list</var></code> clause must be present,
while the <code class="code">otherwise <var class="var">command_list</var></code> clause is optional.
</p>
<p>If <var class="var">label</var> is a cell array the corresponding <var class="var">command_list</var>
is executed if <em class="emph">any</em> of the elements of the cell array match
<var class="var">expression</var>. As an example, the following program will print
‘<samp class="samp">Variable is either 6 or 7</samp>’.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">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></div></div>
<p>As with all other specific <code class="code">end</code> keywords, <code class="code">endswitch</code> may be
replaced by <code class="code">end</code>, but you can get better diagnostics if you use
the specific forms.
</p>
<p>One advantage of using the <code class="code">switch</code> statement compared to using
<code class="code">if</code> statements is that the <var class="var">label</var>s can be strings. If an
<code class="code">if</code> statement is used it is <em class="emph">not</em> possible to write
</p>
<div class="example">
<pre class="example-preformatted">if (X == "a string") # This is NOT valid
</pre></div>
<p>since a character-to-character comparison between <code class="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 class="code">switch</code> statement, and it
is possible to write programs that look like this
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">switch (X)
case "a string"
do_something
...
endswitch
</pre></div></div>
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<li><a href="Notes-for-the-C-Programmer.html" accesskey="1">Notes for the C Programmer</a></li>
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