ascii circles.

circle.rb

def circle(radius: 10)
  0.step(to: radius << 1, by: 1) do |x|
    0.step(to: radius << 1, by: 1) do |y|
      dist = ((x - radius).abs2 + (y - radius).abs2) ** 0.5
      dist.between?(radius - 0.5, radius + 0.5) ? $> << ?. : $> << ' '
    end
    $> << $/
  end
end

5.step to: 20, by: 4 do |radius|
  circle radius: radius
end