The loop() function causes draw() to execute continuously. If noLoop is called in setup() the draw() is only executed once. In this example click the mouse to execute loop(), which will cause the draw() the execute continuously.

Original Example: Loop

// All Examples Written by Casey Reas and Ben Fry
// unless otherwise stated.
// 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 stroke color to white

float y = 100;

// The statements in draw() are run until the 
// program is stopped. Each statement is run in 
// sequence and after the last line is read, the first 
// line is run again.
void draw() 
  background(0);   // Set the background to black
  line(0, y, width, y);  
  y = y - 1; 
  if (y < 0) { 
    y = height; 

void mousePressed()