Processing code for concentric circles using "while"

size(400,400);
smooth();
background(255);

int i = 0;
float y = 300;
float x = 300;
while(i < 150) {
ellipseMode(CENTER);
ellipse(200,200,x,y);
x = x - 30;
y = y - 30;
i = i + 15;
}

--I am currently having trouble making the interactive code work.