Subj : Re: Math error ??? doen't make sense!
To   : borland.public.cpp.borlandcpp
From : Stan DeGroff
Date : Sun Jul 04 2004 12:12 am

Sorry,
This was not explained in the operator descriptions at all.  The Sams book
and several other I've been using (like most of 'em today) do not do a good
job of explaining what they are teaching.  The original code I presented
(other than the unsigned integer format in the print statement) was as
presented in the book.  My experience in assembly and/or PLC programming
would have taken two 16 bit integers and expected a 32 bit result without
having to type cast. I would only need to provide a 32 bit location/register
for the result.  No mention of any intermediate storage considerations being
required.

Thanks for the help Wayne.

Stan


"Wayne A. King" <waking@idirect.com> wrote in message
news:40e602cc.378378@newsgroups.borland.com...
> On Fri, 2 Jul 2004 20:31:26 -0400, "Stan DeGroff" <sdegroff@bright.net>
wrote:
>
> >There ain't no overflow. as shown in the z result above.
>
> As I already explained, the overflow and truncation occur as
> the result of the product exceeding the capacity of a 16-bit int.
> Since both x and y are 16-bit ints, the *intermediate* result will
> be stored in a 16-bit int. The typecast I showed forces promotion
> to 32-bit long for the calculation. The multiplication occurs *before*
> the assignment to a 32-bit long, hence its size is not relevant to
> the capacity used for the product.
>
> >Multiply in Borland product must have both inputs to a multiply
> >and the output all the same size variables.
>
> It depends on the values being stored. Also, promoting one of
> either the multiplier or multiplicand results in automatic promotion
> of the other and of the intermediate temporary variable used for
> the result. This is the way it is in the C and C++ languages. It is not
> unique to Borland. See the C FAQ at
> http://www.eskimo.com/~scs/C-faq/faq.html
> especially 3.14:
>
> "Why doesn't the code
> int a = 1000, b = 1000;
> long int c = a * b;
> work? "
>
> http://www.eskimo.com/~scs/C-faq/q3.14.html
>
>
> --
> Wayne A. King
> (waking@idirect.com, Wayne_A_King@compuserve.com)

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