int x = 0;
int speed = 5;
void setup()
{
size(500,500);
background(122,122,122);

}

void draw()
{
background(122,122,122);
for (int i = 0 ; i < 10; i++)
{
for (int j = 0 ; j < 10; j++)
{

fill(int(random(255)),int(random(255)),int(random(255)));
rect(i*50+x,j*50,50,50);

}
}
x+=speed;

if (x == 500) speed = - speed;

if (x == 0 && speed < 0) speed = -speed;

}