10 G:CLEAR; FULL; PEN BLACK 20 FOR X=-79 TO 80 30 C:NL=NL+1 40 C(NL>9):PN=PN+1 50 G(NL>9):PEN PN 60 C(NL>9):NL=0 70 G:LINE X,100 TO X,-99 80 NEXT 90 A: 100 G:QUIT 110 H: