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<p class='vspace'></p><h2>Static</h2>
<p>The static keyword is used to create variables that are visible to only one function. However unlike local variables that get created and destroyed every time a function is called, static variables persist beyond the function call, preserving their data between function calls.
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<p class='vspace'></p><p>Variables declared as static will only be created and initialized the first time a function is called.
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<p class='vspace'></p><h4>Example</h4>
<pre>
/* RandomWalk
* Paul Badger 2007
* RandomWalk wanders up and down randomly between two
* endpoints. The maximum move in one loop is governed by
* the parameter "stepsize".
* A static variable is moved up and down a random amount.
* This technique is also known as "pink noise" and "drunken walk".
*/
#define randomWalkLowRange -20
#define randomWalkHighRange 20
int stepsize;
int thisTime;
int total;
void setup()
{
Serial.begin(9600);
}
void loop()
{ // tetst randomWalk function
stepsize = 5;
thisTime = randomWalk(stepsize);
Serial.println(thisTime);
delay(10);
}
int randomWalk(int moveSize){
static int place; // variable to store value in random walk - declared static so that it stores
// values in between function calls, but no other functions can change its value
place = place + (random(-moveSize, moveSize + 1));
if (place < randomWalkLowRange){ // check lower and upper limits
place = place + (randomWalkLowRange - place); // reflect number back in positive direction
}
else if(place > randomWalkHighRange){
place = place - (place - randomWalkHighRange); // reflect number back in negative direction
}
return place;
}
</pre>
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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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