A small processing sketch demonstrating a for loop.

Repeating circles

// Define size of canvas
size(480, 120); 

// Set background color (black)
background(0);

// Anti-alias:
smooth(); 

// making shapes without an outer line: 
noStroke(); 

// For loop drawing circles on black background: 
for (int y = 0; y <= height; y += 40) {
  for (int x = 0; x <= width; x += 40) {
    //color of circles 
    fill(255, 140); 
    ellipse(x, y, 40, 40);
    fill(219, 51, 85);
    ellipse(x, y, 30, 30);
    fill(139,135, 136);
    ellipse(x, y, 20, 20);
  }