// Learning Processing
  // Daniel Shiffman
  // http://www.learningprocessing.com
  
  // Example 9-8: A snake following the mouse
  
  // Declare two arrays with 50 elements.
  int[] xpos = new int[50]; 
  int[] ypos = new int[50];
  
  void setup() {
    size(200,200);
    
    smooth();
    // Initialize all elements of each array to zero.
    for (int i = 0; i < xpos.length; i ++ ) {
      xpos[i] = 0; 
      ypos[i] = 0;
    }
  }
  
  void draw() {
    background(255);
    
    // Shift array values
    for (int i = 0; i < xpos.length-1; i ++ ) {
      // Shift all elements down one spot. 
      // xpos[0] = xpos[1], xpos[1] = xpos = [2], and so on. Stop at the second to last element.
      xpos[i] = xpos[i+1];
      ypos[i] = ypos[i+1];
    }
    
    // New location
    xpos[xpos.length-1] = mouseX; // Update the last spot in the array with the mouse location.
    ypos[ypos.length-1] = mouseY;
    
    // Draw everything
    for (int i = 0; i < xpos.length; i ++ ) {
       // Draw an ellipse for each element in the arrays. 
       // Color and size are tied to the loop's counter: i.
      noStroke();
      fill(255-i*5);
      ellipse(xpos[i],ypos[i],i,i);
    }
  }