LIGHTCYCLES.BAS

10 REM LIGHTCYCLES
20 GR:HOME: FOR CLR = 2 TO 13
30 SX=0:SY=0:EX=39:EY=39:COLOR=CLR
40 FOR A = SX TO EX - 1: PLOT A, SY: NEXT A
50 FOR B = SY TO EY - 1: PLOT EX, B: NEXT B
60 FOR C = EX TO SX + 1 STEP -1: PLOT C, EY: NEXT C
70 FOR D = EY TO SY + 1 STEP -1: PLOT SX, D: NEXT D
80 SX=SX+1:SY=SY+1:EX=EX-1:EY=EY-1
90 IF SX>EX THEN GOTO 110
100 GOTO 40
110 NEXT CLR