1 REM X,Y = coordinates of the ball
2 REM XN = the new X coordinate
3 REM YN = the new Y coordinate
4 REM XD = the X direction of motion
5 REM YD = the Y direction of motion (for each space in the X direction)
6 REM
10 GR : COLOR= 3
20 VLIN O,39 AT 19: VLIN 0,39 AT 21
30 X = 0:Y = 0
40 XD = 1:YD = 1
50 COLOR= 5: PLOT X,Y
60 XN = X +XD
70 IF XN = 0 THEN XD = 1
80 IF XN = 39 THEN XD = - 1
90 YN = Y + YD
100 IF YN < 0 THEN YD = INT (2 * RND (1) + 1):YN = Y + YD: GOTO 100
110 IF YN > 39 THEN YD = - INT (2 * RND (1) + 1):YN = Y + Y + YD: GOTO 110
120 IF SCRN( XN,YN) = 3 THEN XD = - 1 * XD
130 COLOR= 0: PLOT X,Y
140 X = XN:Y = YN
150 GOTO 50