// Learning Processing
  // Daniel Shiffman
  // http://www.learningprocessing.com
  
  // Example 5-8: Square following edge, uses a ÒstateÓ variable
  
  int x = 0;  // x location of square
  int y = 0;  // y location of square
  
  int speed = 5;  // speed of square
  
  // A variable to keep track of the squareÕs "state."  
  // Depending on the value of its state, it will either move right, down, left, or up.
  int state = 0;  
  
  void setup() {
    size(200,200);
  }
  
  void draw() {
    background(255);
  
    // Display the square
    stroke(0);
    fill(175);
    rect(x,y,9,9);
  
    // If the state is 0, move to the right.
    if (state == 0) {
      x = x + speed;
      // If, while the state is 0, it reaches the right side of the window, change the state to 1
      // Repeat this same logic for all states!?
      if (x > width-10) {
        x = width-10;
        state = 1;
      }
    } else if (state == 1) {
      y = y + speed;
      if (y > height-10) {
        y = height-10;
        state = 2;
      }
    } else if (state == 2) {
      x = x - speed;
      if (x < 0) {
        x = 0;
        state = 3;
      }
    } else if (state == 3) {
      y = y - speed;
      if (y < 0) {
        y = 0;
        state=0;
      }
    }
  }