'===========================================================================
' Subject: DRAW A CARTIOID                   Date: 12-14-98 (14:35)       
' Author:  Dave Navarro, Jr.                 Code: QB, QBasic, PDS        
' Origin:  dave@powerbasic.com             Packet: GRAPHICS.ABC
'===========================================================================
' Draw a Cartioid
' From "Microcomputer Graphics Techniques and Applications" by Donald Hearn
' ported to PB by Dave Navarro (dave@powerbasic.com)

SCREEN 12

WINDOW (-160, -120) - (160, 120)
XN = 40 : YN = 0
C1 = COS(.314) : S1 = SIN(.314)
FOR I = 1 TO 10
  T = XN*C1 - YN*S1
  YN = XN*S1 + YNC1 : XN = T
  RAD = SQR((XN - 40)^2 + YN ^ 2)
  CIRCLE (XN, YN), RAD
  YL = - YN
  CIRCLE (XN, YL), RAD
NEXT
SLEEP