function putpixel(x,y)
  term.setCursorPos(x, y)
  term.write("@")
end


function drawCircle(x0,y0,radius)
  local x = radius-1
  local y = 0
  local dx = 1
  local dy = 1
  local err = dx - (bit.lshift(radius,1))
  while x >= y do
    putpixel(x0 + x, y0 + y)
    putpixel(x0 + y, y0 + x)
    putpixel(x0 - y, y0 + x)
    putpixel(x0 - x, y0 + y)
    putpixel(x0 - x, y0 - y)
    putpixel(x0 - y, y0 - x)
    putpixel(x0 + y, y0 - x)
    putpixel(x0 + x, y0 - y)
    if err <= 0 then
      y = y + 1
      err = err + dy;
      dy = dy + 2;
    if err > 0 then
      x = x - 1
      dx = dx + 2
      err = err + (bit.lshift(-radius,1)+dx)
    end
  end
end

drawCircle(10,10,10)
read()