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<title>Arduino Reference - Const </title>
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<div class="title"><a href='http://arduino.cc/en'>Arduino</a></div>
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<p><strong>Reference</strong> <a class='wikilink' href='index.html'>Language</a> | <a class='wikilink' href='Libraries.html'>Libraries</a> | <a class='wikilink' href='Comparison.html'>Comparison</a> | <a class='wikilink' href='Changes.html'>Changes</a>
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<p class='vspace'></p><h2>const keyword</h2>
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<p>The <strong>const</strong> keyword stands for constant. It is a variable <em>qualifier</em> that modifies the behavior of the variable, making a variable "<em>read-only</em>". This means that the variable can be used just as any other variable of its type, but its value cannot be changed. You will get a compiler error if you try to assign a value to a <strong>const</strong> variable.
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<p class='vspace'></p><p>Constants defined with the <em>const</em> keyword obey the rules of <em><a class='wikilink' href='Scope.html'>variable scoping</a></em> that govern other variables. This, and the pitfalls of using<em>#define</em>, makes the <em>const</em> keyword a superior method for defining constants and is preferred over using <em><a class='wikilink' href='Define.html'>#define</a></em>.
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<p class='vspace'></p><h4>Example</h4>
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<pre>
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const float pi = 3.14;
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float x;
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// ....
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x = pi * 2; // it's fine to use const's in math
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pi = 7; // illegal - you can't write to (modify) a constant
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</pre><h4><strong>#define</strong> or <strong>const</strong></h4>
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<p>You can use either <strong>const</strong> or <strong>#define</strong> for creating numeric or string constants. For <a class='wikilink' href='Array.html'>arrays</a>, you will need to use <strong>const</strong>. In general <em>const</em> is preferred over <em>#define</em> for defining constants.
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<p class='vspace'></p><p>See also:
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</p><ul><li><a class='wikilink' href='Define.html'>#define</a>
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</li><li><a class='wikilink' href='Volatile.html'>volatile</a>
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</li></ul><p><a class='wikilink' href='index.html'>Reference Home</a>
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<p class='vspace'></p><p><em>Corrections, suggestions, and new documentation should be posted to the <a class='urllink' href='http://arduino.cc/forum/index.php/board,23.0.html' rel='nofollow'>Forum</a>.</em>
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<p class='vspace'></p><p>The text of the Arduino reference is licensed under a
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<a class='urllink' href='http://creativecommons.org/licenses/by-sa/3.0/' rel='nofollow'>Creative Commons Attribution-ShareAlike 3.0 License</a>. Code samples in the reference are released into the public domain.
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