Re: Factorial

From: Wes Spikes (MornThdr_at_NOSPAMverizon.net)
Date: 05/22/04 

Date: Sat, 22 May 2004 21:00:21 GMT

Ok, I'm trying to use it now (sorry for not trying it earlier --I'm a little
absent-minded), but x is undefined (I've made it a practice to use Option
Explicit), so I'm going to try and use it as an integer!

-Wes

"Rick Rothstein" <rickNOSPAMnews@NOSPAMcomcast.net> wrote in message
news:e8B#iptPEHA.2704@TK2MSFTNGP10.phx.gbl...
> > Oops, to avoid overflow, do this instead:
> >
> > Public Function Factorial(x As Integer) As Double
> > Factorial = 1
> > For I = 0 To x - 1
> > Factorial = Factorial * (x - I)
> > Next I
> > End Function
>
> Perhaps this combination of two posts I given in the past may be of some
> help or interest...
>
> Rick - MVP
>
> You could cast (you can't Dim) a Variant variable as a Decimal type
> (96-bit number) and get some 28 or 29 digits of accuracy depending if
> there is a decimal in the answer or not. Simply Dim a variable as
> Variant and CDec a number (any number will do) into it to make it the
> Decimal type. Thereafter, that variable will track 28/29 digits of
> accuracy. For example the following function will calculate factorials
> up to 29 digits of display before reverting to exponential display.
>
> Function BigFactorial(ByVal N As Integer) As Variant
> If N < 28 Then
> BigFactorial = CDec(1)
> Else
> BigFactorial = CDbl(1)
> End If
> For x = 1 To N
> BigFactorial = x * BigFactorial
> Next
> End Function
>
> However, you have to watch out for overflows with Decimal data types --
> once over 28/29 characters, they will produce an overflow error. So, if
> you tried to use the above function like this
>
> Debug.Print 10*BigFactorial(27)
>
> you would get an overflow error but
>
> Debug.Print 10*BigFactorial(28)
>
> would work fine (the difference being in the first case BigFactorial has
> a Decimal subtype and in the second case the subtype is a Double).
>
> More generally, if a Variant variable is assigned a value that was cast
> to Decimal, any calculation involving that variable will be "performed"
> as a Decimal; and then the result cast back to the variable receiving
> it. If the result is assigned back to the variable that was originally
> cast to Decimal, that variable continues to contain a Decimal type
> value. For example,
>
> X = CDec(135.6)
> X = X - 135
> X = X / 7
> Print X ==> 0.0857142857142857142857142857
>
> You have to be careful with this though . . . all VB functions return
> non-Decimal data.and assigning *that* back to the Variant that was cast
> as Decimal "collapses" it back to a less robust data type. For example,
> continuing the code above
>
> X = Sqr(X)
> Print X ==> 0.29277002188456
>

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