Arduino

Reference Language | Libraries | Comparison | Changes

## 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()
    {        //  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;
    }

Reference Home

Corrections, suggestions, and new documentation should be posted to the Forum.

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.

©Arduino | Edit Page | Page History | Printable View | All Recent Site Changes