Static

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.

Variables declared as static will only be created and initialized the first time a function is called.

Example

/* 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(){        //  test 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;
}

The text of the Arduino reference is licensed under a Creative Commons Attribution-ShareAlike 3.0 License. Code samples in the reference are released into the public domain.