function circle(r,color)
x = 0;
y = r;
sfalma = 3 - 2 * r;
hold on
while x <= y
    image(x,y,color)
    x = x + 1;
    if sfalma >= 0
        y = y - 1;
        sfalma = sfalma - 4 * y;
    end
    sfalma = sfalma + 4 * x + 2;
end
axis equal