141 lines
6.2 KiB
HTML
141 lines
6.2 KiB
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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='Board.html'>Board</a>
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</p>
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<p class='vspace'></p><h2>Functions</h2>
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<p>Segmenting code into functions allows a programmer to create modular pieces of code that perform a defined task and then return to the area of code from which the function was "called". The typical case for creating a function is when one needs to perform the same action multiple times in a program.
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</p>
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<p class='vspace'></p><p>For programmers accustomed to using BASIC, functions in Arduino provide (and extend) the utility of using subroutines (GOSUB in BASIC).
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</p>
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<p class='vspace'></p><p>Standardizing code fragments into functions has several advantages:
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</p>
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<p class='vspace'></p><ul><li>Functions help the programmer stay organized. Often this helps to conceptualize the program.
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<p class='vspace'></p></li><li>Functions codify one action in one place so that the function only has to be thought out and debugged once.
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<p class='vspace'></p></li><li>This also reduces chances for errors in modification, if the code needs to be changed.
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<p class='vspace'></p></li><li>Functions make the whole sketch smaller and more compact because sections of code are reused many times.
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<p class='vspace'></p></li><li>They make it easier to reuse code in other programs by making it more modular, and as a nice side effect, using functions also often makes the code more readable.
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</li></ul><p class='vspace'></p><p>There are two required functions in an Arduino sketch, setup() and loop(). Other functions must be created outside the brackets of those two functions. As an example, we will create a simple function to multiply two numbers.
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</p>
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<p class='vspace'></p><h4>Example</h4>
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<div><img src='http://www.arduino.cc/en/uploads/Reference/FuncAnatomy.png' alt='' title='' /></div>
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<p class='vspace'></p><p>To "call" our simple multiply function, we pass it parameters of the datatype that it is expecting:
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</p>
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<p class='vspace'></p><pre>
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void loop{
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int i = 2;
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int j = 3;
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int k;
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k = myMultiplyFunction(i, j); // k now contains 6
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}
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</pre><p>Our function needs to be <em>declared</em> outside any other function, so "myMultiplyFunction()" can go either above or below the "loop()" function.
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</p>
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<p class='vspace'></p><p>The entire sketch would then look like this:
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</p><pre>void setup(){
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Serial.begin(9600);
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}
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void loop{
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int i = 2;
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int j = 3;
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int k;
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k = myMultiplyFunction(i, j); // k now contains 6
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Serial.println(k);
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delay(500);
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}
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int myMultiplyFunction(int x, int y){
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int result;
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result = x * y;
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return result;
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}
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</pre>
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<p class='vspace'></p><h4>Another example </h4>
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<p>This function will read a sensor five times with analogRead() and calculate the average of five readings. It then scales the data to 8 bits (0-255), and inverts it, returning the inverted result.
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</p>
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<p class='vspace'></p><pre>int ReadSens_and_Condition(){
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int i;
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int sval;
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for (i = 0; i < 5; i++){
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sval = sval + analogRead(0); // sensor on analog pin 0
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}
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sval = sval / 5; // average
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sval = sval / 4; // scale to 8 bits (0 - 255)
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sval = 255 - sval; // invert output
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return sval;
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}
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</pre>
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<p class='vspace'></p><p>To call our function we just assign it to a variable.
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</p>
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<p class='vspace'></p><pre>int sens;
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sens = ReadSens_and_Condition();
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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 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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