2020-12-15 03:48:17 +00:00
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400 GR : REM SET COLOR GRAPHICS AREA
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420 HOME : REM CLEAR TEXT AREA
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440 X = 0: REM SET STARTING POSITION OF BACK-AND-FORTH VARIABLE
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460 Y = 5: REM SET STARTING POSITION OF UP-AND-DOWN VARIABLE
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480 XV = 2: REM SET X VELOCITY
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500 YV = 1: REM SET Y VELOCITY
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520 REM CALCULATE NEW POSITION
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540 NX = X + XV:NY = Y + YV
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560 REM IF BALL EXCEEDS SCREEN EDGE, THEN BOUNCE
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580 IF NX > 39 THEN NX = 39:XV = - XV
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600 IF NX < 0 THEN NX = 0:XV = - XV
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620 IF NY > 39 THEN NY = 39:YV = - YV
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640 IF NY < 0 THEN NY = 0:YV = - YV
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660 REM PLOT NEW POSITION
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680 COLOR= 7: PLOT NX,NY
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700 REM ERASE OLD POSITION
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720 COLOR= 0: PLOT X,Y
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740 REM SAVE CURRENT POSITION
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760 X = NX:Y = NY
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780 GOTO 540
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