' Fibonacci sequence

BEGIN DEF
pointer dword FibPtr~ ' Why "pointer dword" must be in lower case?
SUB CalcFib(N%, FibPtr~)

BEGIN CODE
PRINT "Enter n for fib(n): "
INPUT SN$
N% = VAL(SN$)
PRINT "\n"
CALL CalcFib(N%, VARPTR(Fib&))
PRINT Fib& + "\n"
END

SUB CalcFib(N%, FibPtr~)
IF N% = 0 THEN
  Fib& = 0
ELSE
  IF N% = 1 THEN
    Fib& = 1
  ELSE
    Prev& = 0
    Fib& = 1
    FOR I% = 2 TO N%
      T& = Fib&
      Fib& = Prev& + Fib&
      Prev& = T&
    NEXT
  ENDIF
ENDIF
[FibPtr~] = Fib&
END SUB