// The statements in the setup() function 
  // execute once when the program begins
  void setup() 
  {
    size(200, 200);  // Size should be the first statement
    stroke(255);     // Set line drawing color to white
    noLoop();
  }
  
  float y = 100;
  
  // The statements in draw() are executed until the 
  // program is stopped. Each statement is executed in 
  // sequence and after the last line is read, the first 
  // line is executed again.
  void draw() 
  { 
    background(0);   // Set the background to black
    y = y - 1; 
    if (y < 0) { y = height; } 
    line(0, y, width, y);  
  } 
  
  void mousePressed() 
  {
    redraw();
  }