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140 lines
5.3 KiB
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<title>Arduino Reference - Random </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>
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<p class='vspace'></p><h2>random()</h2>
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<h4>Description</h4>
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<p>The random function generates pseudo-random numbers.
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</p>
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<p class='vspace'></p><h4>Syntax</h4>
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<p>random(max)<br />random(min, max)
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</p>
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<p class='vspace'></p><h4>Parameters</h4>
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<p>min - lower bound of the random value, inclusive <em>(optional)</em>
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</p>
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<p class='vspace'></p><p>max - upper bound of the random value, exclusive
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</p>
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<p class='vspace'></p><h4>Returns</h4>
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<p>a random number between min and max-1 (<em>long</em>)
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</p>
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<p class='vspace'></p><h4>Note: </h4>
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<p>If it is important for a sequence of values generated by random() to differ, on subsequent executions of a sketch, use randomSeed() to initialize the random number generator with a fairly random input, such as analogRead() on an unconnected pin.
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</p>
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<p class='vspace'></p><p>Conversely, it can occasionally be useful to use pseudo-random sequences that repeat exactly. This can be accomplished by calling randomSeed() with a fixed number, before starting the random sequence.
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</p>
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<p class='vspace'></p><h4>Example</h4>
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<pre>
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long randNumber;
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void setup(){
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Serial.begin(9600);
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// if analog input pin 0 is unconnected, random analog
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// noise will cause the call to randomSeed() to generate
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// different seed numbers each time the sketch runs.
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// randomSeed() will then shuffle the random function.
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randomSeed(analogRead(0));
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}
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void loop() {
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// print a random number from 0 to 299
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randNumber = random(300);
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Serial.println(randNumber);
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// print a random number from 10 to 19
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randNumber = random(10, 20);
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Serial.println(randNumber);
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delay(50);
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}
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</pre>
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<p class='vspace'></p><h4>See also</h4>
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<ul><li><a class='wikilink' href='RandomSeed.html'>randomSeed</a>()
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</li></ul><p class='vspace'></p><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>
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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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