'\begin{verbatim}
'This program simulates random walk paths (with uniform incerments)
'reflected at the boundaries of a region
'
'declarations of subs
DECLARE SUB CenterPrint (Text$)

' minimal error handling - graphics card is required
ON ERROR GOTO ErrTrap

CLS
'request good graphics (some cards support SCREEN 7, etc)
SCREEN 9

LOCATE 1, 1 'title
CenterPrint "Path of reflected random walk"
LOCATE 9, 1  'timer location
PRINT "Timer"

scale = 10 '
WINDOW (0, 0)-(scale, scale): VIEW (150, 100)-(600, 300)
LINE (0, 0)-(scale, scale), 10, B': LINE (scale, scale)-(2 * scale, 0), 11, B
FOR j = -4 TO 4
LINE (0, scale / 2 + j)-(scale / 50, scale / 2 + j), 2
NEXT j
X = scale / 2
Y = scale / 2
dead = 0
T = 0
col = 14 * RND(1)
speed = scale / 100
WHILE INKEY$ = "" 'infinite loop until a key is pressed
T = T + 1
X0 = X
Y0 = Y
X = X + (RND(1) - 1 / 2) * speed
Y = Y + (RND(1) - 1 / 2) * speed
IF X < 0 THEN X = -X: col = 14 * RND(1)
IF Y < 0 THEN Y = -Y: col = 14 * RND(1)
IF X > scale THEN X = 2 * scale - X: col = 14 * RND(1)
IF Y > scale THEN Y = 2 * scale - Y: col = 14 * RND(1)
IF X > 2 * scale THEN X = 4 * scale - X: col = 14 * RND(1)
LINE (X0, Y0)-(X, Y), col
LOCATE 10, 1
PRINT T
WEND

END

ErrTrap: 'if there are errors then quit
CLS
PRINT "This error requires graphics card VGA"
PRINT "Error running program"
PRINT "Press any key ...'"
WHILE INKEY$ = ""
WEND
END

SUB CenterPrint (Text$)
' Print text centered in 80 column screen
offset = 41 - LEN(Text$) \ 2
IF offset < 1 THEN offset = 1
LOCATE , offset
PRINT Text$
'\end{verbatim}
END SUB