PROC bounce:
	LOCAL posX%,posY%,changeX%,changeY%,k%
	LOCAL scrx%,scry%
	scrx%=40 :scry%=9
	posX%=1	:posY%=1
	changeX%=1 :changeY%=1
	DO
		posX%=posX%+changeX%
		posY%=posY%+changeY%
		IF posX%=1 OR posX%=scrx%
			changeX%=-changeX%
			REM at edge ball changes direction
			BEEP 2, 600 REM low beep
		ENDIF
		IF posY%=1 or posY%=scry% REM same for y
			changeY%=-changeY%
			BEEP 2, 200 REM high beep
		ENDIF
		AT posX%,posY% :PRINT "0";
		PAUSE 2	 REM Try changing this
		AT posX%,posY% :PRINT " ";
		REM removes old `0' character
    	k%=KEY
	UNTIL k%
ENDP