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<hr>
<h2 class="chapter" id="Variables-1"><span>7 Variables<a class="copiable-link" href="#Variables-1"> ¶</a></span></h2>
<a class="index-entry-id" id="index-variables_002c-user_002ddefined"></a>
<a class="index-entry-id" id="index-user_002ddefined-variables"></a>
<p>Variables let you give names to values and refer to them later. You have
already seen variables in many of the examples. The name of a variable
must be a sequence of letters, digits and underscores, but it may not begin
with a digit. Octave does not enforce a limit on the length of variable
names, but it is seldom useful to have variables with names longer than
about 30 characters. The following are all valid variable names
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">x
x15
__foo_bar_baz__
fucnrdthsucngtagdjb
</pre></div></div>
<p>However, names like <code class="code">__foo_bar_baz__</code> that begin and end with two
underscores are understood to be reserved for internal use by Octave.
You should not use them in code you write, except to access Octave’s
documented internal variables and built-in symbolic constants.
</p>
<p>Case is significant in variable names. The symbols <code class="code">a</code> and
<code class="code">A</code> are distinct variables.
</p>
<p>A variable name is a valid expression by itself. It represents the
variable’s current value. Variables are given new values with
<em class="dfn">assignment operators</em> and <em class="dfn">increment operators</em>.
See <a class="xref" href="Assignment-Ops.html">Assignment Expressions</a>.
</p>
<p>There is one automatically created variable with a special meaning. The
<code class="code">ans</code> variable always contains the result of the last computation,
where the output wasn’t assigned to any variable. The code <code class="code">a =
cos (pi)</code> will assign the value -1 to the variable <code class="code">a</code>, but will
not change the value of <code class="code">ans</code>. However, the code <code class="code">cos (pi)</code>
will set the value of <code class="code">ans</code> to -1.
</p>
<p>Variables in Octave do not have fixed types, so it is possible to first
store a numeric value in a variable and then to later use the same name
to hold a string value in the same program. Variables may not be used
before they have been given a value. Doing so results in an error.
</p>
<a class="index-entry-id" id="index-ans"></a>
<a class="anchor" id="XREFans"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-defvr">
<dt class="defvr" id="index-ans-1"><span class="category-def">Automatic Variable: </span><span><strong class="def-name">ans</strong><a class="copiable-link" href="#index-ans-1"> ¶</a></span></dt>
<dd><p>The most recently computed result that was not explicitly assigned to a
variable.
</p>
<p>For example, after the expression
</p>
<div class="example">
<pre class="example-preformatted">3^2 + 4^2
</pre></div>
<p>is evaluated, the value returned by <code class="code">ans</code> is 25.
</p></dd></dl>
<a class="anchor" id="XREFisvarname"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-isvarname"><span><code class="def-type"><var class="var">tf</var> =</code> <strong class="def-name">isvarname</strong> <code class="def-code-arguments">(<var class="var">name</var>)</code><a class="copiable-link" href="#index-isvarname"> ¶</a></span></dt>
<dd><p>Return true if <var class="var">name</var> is a valid variable name.
</p>
<p>A valid variable name is composed of letters, digits, and underscores ("_"),
and the first character must not be a digit.
</p>
<p><strong class="strong">See also:</strong> <a class="ref" href="Keywords.html#XREFiskeyword">iskeyword</a>, <a class="ref" href="Status-of-Variables.html#XREFexist">exist</a>, <a class="ref" href="Status-of-Variables.html#XREFwho">who</a>.
</p></dd></dl>
<a class="anchor" id="XREFmatlab_005flang_005fmakeValidName"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-matlab_002elang_002emakeValidName"><span><code class="def-type"><var class="var">varname</var> =</code> <strong class="def-name">matlab.lang.makeValidName</strong> <code class="def-code-arguments">(<var class="var">str</var>)</code><a class="copiable-link" href="#index-matlab_002elang_002emakeValidName"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-matlab_002elang_002emakeValidName-1"><span><code class="def-type"><var class="var">varname</var> =</code> <strong class="def-name">matlab.lang.makeValidName</strong> <code class="def-code-arguments">(…, <code class="code">"ReplacementStyle"</code>, <var class="var">rs</var>)</code><a class="copiable-link" href="#index-matlab_002elang_002emakeValidName-1"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-matlab_002elang_002emakeValidName-2"><span><code class="def-type"><var class="var">varname</var> =</code> <strong class="def-name">matlab.lang.makeValidName</strong> <code class="def-code-arguments">(…, <code class="code">"Prefix"</code>, <var class="var">pfx</var>)</code><a class="copiable-link" href="#index-matlab_002elang_002emakeValidName-2"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-matlab_002elang_002emakeValidName-3"><span><code class="def-type">[<var class="var">varname</var>, <var class="var">ismodified</var>] =</code> <strong class="def-name">matlab.lang.makeValidName</strong> <code class="def-code-arguments">(…)</code><a class="copiable-link" href="#index-matlab_002elang_002emakeValidName-3"> ¶</a></span></dt>
<dd>
<p>Create valid variable name <var class="var">varname</var> from <var class="var">str</var>.
</p>
<p>The input <var class="var">str</var> must be a string or a cell array of strings.
The output <var class="var">varname</var> will be of the same type.
</p>
<p>A valid variable name is a sequence of letters, digits, and underscores that
does not begin with a digit.
</p>
<p>The <code class="code">"ReplacementStyle"</code> option specifies how invalid characters
are handled. Acceptable values are
</p>
<dl class="table">
<dt><code class="code">"underscore"</code> (default)</dt>
<dd><p>Replace all invalid characters with an underscore (<code class="code">"_"</code>).
</p>
</dd>
<dt><code class="code">"delete"</code></dt>
<dd><p>Remove any invalid character.
</p>
</dd>
<dt><code class="code">"hex"</code></dt>
<dd><p>Replace all invalid characters with their hexadecimal representation.
</p></dd>
</dl>
<p>Whitespace characters are always removed <strong class="strong">prior</strong> to the application
of the <code class="code">"ReplacementStyle"</code>. Lowercase letters following a whitespace
will be changed to uppercase.
</p>
<p>The <code class="code">"Prefix"</code> option specifies the string <var class="var">pfx</var> to add as a
prefix to the input if it begins with a digit. <var class="var">pfx</var> must be a valid
variable name itself. The default prefix is <code class="code">"x"</code>.
</p>
<p>The optional output <var class="var">ismodified</var> is a logical array indicating whether
the respective element in <var class="var">str</var> was a valid name or not.
</p>
<p><strong class="strong">See also:</strong> <a class="ref" href="Keywords.html#XREFiskeyword">iskeyword</a>, <a class="ref" href="#XREFisvarname">isvarname</a>, <a class="ref" href="#XREFmatlab_005flang_005fmakeUniqueStrings">matlab.lang.makeUniqueStrings</a>.
</p></dd></dl>
<a class="anchor" id="XREFmatlab_005flang_005fmakeUniqueStrings"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-matlab_002elang_002emakeUniqueStrings"><span><code class="def-type"><var class="var">uniqstr</var> =</code> <strong class="def-name">matlab.lang.makeUniqueStrings</strong> <code class="def-code-arguments">(<var class="var">str</var>)</code><a class="copiable-link" href="#index-matlab_002elang_002emakeUniqueStrings"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-matlab_002elang_002emakeUniqueStrings-1"><span><code class="def-type"><var class="var">uniqstr</var> =</code> <strong class="def-name">matlab.lang.makeUniqueStrings</strong> <code class="def-code-arguments">(<var class="var">str</var>, <var class="var">ex</var>)</code><a class="copiable-link" href="#index-matlab_002elang_002emakeUniqueStrings-1"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-matlab_002elang_002emakeUniqueStrings-2"><span><code class="def-type"><var class="var">uniqstr</var> =</code> <strong class="def-name">matlab.lang.makeUniqueStrings</strong> <code class="def-code-arguments">(<var class="var">str</var>, <var class="var">ex</var>, <var class="var">maxlength</var>)</code><a class="copiable-link" href="#index-matlab_002elang_002emakeUniqueStrings-2"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-matlab_002elang_002emakeUniqueStrings-3"><span><code class="def-type">[<var class="var">uniqstr</var>, <var class="var">ismodified</var>] =</code> <strong class="def-name">matlab.lang.makeUniqueStrings</strong> <code class="def-code-arguments">(…)</code><a class="copiable-link" href="#index-matlab_002elang_002emakeUniqueStrings-3"> ¶</a></span></dt>
<dd>
<p>Construct a list of unique strings from a list of strings.
</p>
<p>The input <var class="var">str</var> must be a string or a cell array of strings.
The output <var class="var">uniqstr</var> will be of the same type.
</p>
<p>The algorithm makes two strings unique by appending an underscore
(<code class="code">"_"</code> and a numeric count to the second string.
</p>
<p>If <var class="var">ex</var> is a string or a cell array of strings, <var class="var">uniqstr</var> will
contain elements that are unique between themselves and with respect to
<var class="var">ex</var>.
</p>
<p>If <var class="var">ex</var> is an index array or a logical array for <var class="var">str</var> then it
selects the subset of <var class="var">str</var> that are made unique. Unselected elements
are not modified.
</p>
<p>The optional input <var class="var">maxlength</var> specifies the maximum length of any
string in <var class="var">uniqstr</var>. If an input string cannot be made unique without
exceeding <var class="var">maxlength</var> an error is emitted.
</p>
<p>The optional output <var class="var">ismodified</var> is a logical array indicating whether
each element in <var class="var">str</var> was modified to make it unique.
</p>
<p><strong class="strong">See also:</strong> <a class="ref" href="Sets.html#XREFunique">unique</a>, <a class="ref" href="#XREFmatlab_005flang_005fmakeValidName">matlab.lang.makeValidName</a>.
</p></dd></dl>
<a class="anchor" id="XREFnamelengthmax"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-namelengthmax"><span><code class="def-type"><var class="var">n</var> =</code> <strong class="def-name">namelengthmax</strong> <code class="def-code-arguments">()</code><a class="copiable-link" href="#index-namelengthmax"> ¶</a></span></dt>
<dd><p>Return the <small class="sc">MATLAB</small> compatible maximum variable name length.
</p>
<p>Octave is capable of storing strings up to <em class="math">2^{31} - 1</em> in length.
However for <small class="sc">MATLAB</small> compatibility all variable, function, and structure
field names should be shorter than the length returned by
<code class="code">namelengthmax</code>. In particular, variables stored to a <small class="sc">MATLAB</small> file
format (<samp class="file">*.mat</samp>) will have their names truncated to this length.
</p></dd></dl>
<ul class="mini-toc">
<li><a href="Global-Variables.html" accesskey="1">Global Variables</a></li>
<li><a href="Persistent-Variables.html" accesskey="2">Persistent Variables</a></li>
<li><a href="Status-of-Variables.html" accesskey="3">Status of Variables</a></li>
</ul>
</div>
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