Event and Error Trapping
 
The following program shows how to trap an event that occurs while a
program is running. With event trapping, you can get your program to
detect run-time events such as keystrokes.
 
Example 1 - Event Trapping
 
If you use a 101-key keyboard, you can trap any of the keys on the
dedicated keypad by assigning the string
 
  CHR$(128) + CHR$(scancode)
 
to any of the keynumber values from 15 to 25.
 
The next example shows how to trap the LEFT direction keys on both
the dedicated cursor keypad and the numeric keypad.
 
  ' 128 = keyboard flag for keys on the
  '       dedicated cursor keypad
  '  75 = scan code for LEFT arrow key
  '
  KEY 15, CHR$(128) + CHR$(75)    ' Trap LEFT key on
  ON KEY(15) GOSUB CursorPad      ' the dedicated
  KEY(15) ON                      ' cursor keypad.
 
  ON KEY(12) GOSUB NumericPad     ' Trap LEFT key on
  KEY(12) ON                      ' the numeric keypad.
 
  DO
  LOOP UNTIL INKEY$ = "q"          ' Idle loop
  END
 
  CursorPad:
    PRINT "Pressed LEFT key on cursor keypad."
  RETURN
 
  NumericPad:
    PRINT "Pressed LEFT key on numeric keypad."
  RETURN