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97 lines
4.5 KiB
HTML
97 lines
4.5 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html>
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<head>
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<title>Arduino - Scope </title>
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<div class="title"><a href="http://www.arduino.cc"/>Arduino</a></div>
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<p><a class='wikilink' href='http://arduino.cc/en/Main/Buy'>Buy</a>
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<a class='wikilink' href='http://arduino.cc/en/Main/Hardware'>Hardware</a>
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<p class='vspace'></p>
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<a class="urllink" href="http://www.arduino.cc/blog/" rel="nofollow">Blog »</a> |
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<p><strong>Reference</strong> <a class='wikilink' href='index.html'>Language</a> (<a class='wikilink' href='Extended.html'>extended</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>
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<p class='vspace'></p><h2>Variable Scope</h2>
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<p>Variables in the C programming language, which Arduino uses, have a property called <em>scope</em>. This is in contrast to languages such as BASIC where every variable is a <em>global</em> variable.
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</p>
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<p class='vspace'></p><p>A global variable is one that can be <em>seen</em> by every function in a program. Local variables are only visible to the function in which they are declared. In the Arduino environment, any variable declared outside of a function (e.g. setup(), loop(), etc. ), is a global variable.
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</p>
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<p class='vspace'></p><p>When programs start to get larger and more complex, local variables are a useful way to insure that only one function has access to its own variables. This prevents programming errors when one function inadvertently modifies variables used by another function.
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</p>
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<p class='vspace'></p><p>It is also sometimes handy to declare and initialize a variable inside a <em>for</em> loop. This creates a variable that can only be accessed from inside the for-loop brackets.
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</p>
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<p class='vspace'></p><h4>Example:</h4>
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<pre>int gPWMval; // any function will see this variable
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void setup()
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{
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// ...
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}
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void loop()
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{
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int i; // "i" is only "visible" inside of "loop"
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float f; // "f" is only "visible" inside of "loop"
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// ...
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for (int j = 0; j <100; j++){
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// variable j can only be accessed inside the for-loop brackets
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}
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}
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</pre>
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<p class='vspace'></p><p><a class='wikilink' href='index.html'>Reference Home</a>
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</p>
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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://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?board=swbugs' rel='nofollow'>Forum</a>.</em>
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</p>
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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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