10 LET x=3: LET y=0: LET d=1: LET e=1
20 LET x=x+d: LET y=y+e: PRINT AT x,y;"*": IF x>=18 OR x<=0 THEN LET d=d*-1
23 IF y>=18 OR y <=0 THEN LET e=e*-1
24 IF x=9 AND y=0 THEN LET x=1
25 IF x=3 AND y=0 THEN LET x=9 
30 GO TO 20