Random X and Y

int num_squares = 200;

int[] x_values = new int[num_squares];

int[] y_values = new int[num_squares]; 

void setup() {

  size(600, 400);

  for (int i = 0; i<x_values.length; i++) {

    x_values[i] = int( random(width) );

    y_values[i] = int( random(height) );

  }

}

void draw() {

  background(40, 200, 140);

  for (int i = 0; i<x_values.length; i++) {

    rect(x_values[i]+(mouseX*.005)*i, y_values[i], 30, 30);

  }

}