// Example: Using for loops to draw rectangles

void setup ()
{
  size(300, 300);
  background(10);
  frameRate(5);
}

void draw ()
{
  drawBoxes();
}

// Simple function: no input, no output returned
void drawBoxes ()
{
  int x;
  int y = 25;
  int maxRects = 5;
  int maxRows = 5;
  
  // For each row in the image...
  for (int row = 0; row < maxRows; row++)
  {
    x = 25;
    
    // Draw a number of squares corresponding to
    // that row's value (i.e., 1 square for the
    // first row (row 0), 2 squares for the second
    // row, etc...)
    for (int numRects = 0; numRects < (row + 1); numRects++)
    // To draw a "square" of squares, replace "(row + 1)"
    // with "maxRows" in the loop test above
    {
      fill(random(256), random(256), random(256));
      rect(x, y, 50,50);
      x = x + 50; // Move to right of last rectangle
    }
    y = y + 50; // Move down 1 row
  }
}