<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html> <head> <title>Arduino - Scope </title> <link rel='stylesheet' href='arduino.css' type='text/css' /> <meta name="verify-v1" content="TtxFIEJAB6zdJ509wLxjnapQzKAMNm9u0Wj4ho6wxIY=" /> </head> <body> <div id="page"> <!--PageHeaderFmt--> <div id="pageheader"> <div class="title"><a href="http://www.arduino.cc"/>Arduino</a></div> <div class="search"> <!-- SiteSearch Google --> <FORM method=GET action="http://www.google.com/search"> <input type=hidden name=ie value=UTF-8> <input type=hidden name=oe value=UTF-8> <INPUT TYPE=text name=q size=25 maxlength=255 value=""> <INPUT type=submit name=btnG VALUE="search"> <input type=hidden name=domains value="http://www.arduino.cc/"> <input type=hidden name=sitesearch value="http://www.arduino.cc/"> </FORM> <!-- SiteSearch Google --> </div> </div> <!--/PageHeaderFmt--> <!--PageLeftFmt--> <div id="pagenav" style="text-align: right"> <div style="float: left;"> <p><a class='wikilink' href='http://arduino.cc/en/Main/Buy'>Buy</a> | <a class='wikilink' href='http://arduino.cc/en/Main/Software'>Download</a> | <a class='wikilink' href='Guide_index.html'>Getting Started</a> | <a class='wikilink' href='http://arduino.cc/en/Tutorial/HomePage'>Learning</a> | <a class='wikilink' href='index.html'>Reference</a> | <a class='wikilink' href='http://arduino.cc/en/Main/Hardware'>Hardware</a> | <a class='wikilink' href='FAQ.html'>FAQ</a> </p> <p class='vspace'></p> </div> <a class="urllink" href="http://www.arduino.cc/blog/" rel="nofollow">Blog »</a> | <a class="urllink" href="http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl" rel="nofollow">Forum »</a> | <a class="urllink" href="http://www.arduino.cc/playground/" rel="nofollow">Playground »</a> </div> <!--/PageLeftFmt--> <div id="pagetext"> <!--PageText--> <div id='wikitext'> <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> </p> <p class='vspace'></p><h2>Variable Scope</h2> <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. </p> <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. </p> <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. </p> <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. </p> <p class='vspace'></p><h4>Example:</h4> <pre>int gPWMval; // any function will see this variable void setup() { // ... } void loop() { int i; // "i" is only "visible" inside of "loop" float f; // "f" is only "visible" inside of "loop" // ... for (int j = 0; j <100; j++){ // variable j can only be accessed inside the for-loop brackets } } </pre> <p class='vspace'></p><p><a class='wikilink' href='index.html'>Reference Home</a> </p> <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> </p> <p class='vspace'></p><p>The text of the Arduino reference is licensed under a <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. </p> </div> </div> <!--PageFooterFmt--> <div id="pagefooter"> <a href='#'>Edit Page</a> | <a href='#'>Page History</a> | <a href='#' target='_blank'>Printable View</a> | <a href='http://arduino.cc/en/Site/AllRecentChanges'>All Recent Site Changes</a> </div> <!--/PageFooterFmt--> </div> </body> </html>