255 * 255 calculation

[Miroslav St. Jeliaskoff]

Why I can't get this result?

Label1.Capton = 255 * 255

Isn't it strange? Atleast for me it is!

Miroslav St. Jeliaskoff

[Bob Butler]

"Miroslav St. Jeliaskoff" <miroslav@earthling.net> wrote in message
news:3d305378$1@10.1.10.29
> Why I can't get this result?
>
> Label1.Capton = 255 * 255
>
> Isn't it strange? Atleast for me it is!

255 fits into a 16-bit integer so that's what VB uses to store the constant.
The largest data type in '255*255' is a 16-bit integer so that's what VB
uses to hold the result.
255*255> 32767 so there is an overflow error.

To get around this promote at least one value to a larger type:

Label1.Caption=CStr(255 * 255&)
or
Label1.Caption=CStr(255 * CLng(255))

Note: the CStr is not required as VB will coerce the numeric result to a
string to put it into the caption; I just prefer to make all data
conversions explicit rather than relying on VB to guess what I mean.

[Miroslav St. Jeliaskoff]

Thanks Bob,
I didn't know that. If I understand Atleast one of the arguments
in that function has to be of a bigger type?

Miroslav St. Jeliaskoff

"Bob Butler" <butlerbob@earthlink.net> wrote in message
news:3d30546a@10.1.10.29...
> "Miroslav St. Jeliaskoff" <miroslav@earthling.net> wrote in
message
> news:3d305378$1@10.1.10.29
> > Why I can't get this result?
> >
> > Label1.Capton = 255 * 255
> >
> > Isn't it strange? Atleast for me it is!
>
> 255 fits into a 16-bit integer so that's what VB uses to store
the constant.
> The largest data type in '255*255' is a 16-bit integer so that's
what VB
> uses to hold the result.
> 255*255> 32767 so there is an overflow error.
>
> To get around this promote at least one value to a larger type:
>
> Label1.Caption=CStr(255 * 255&)
> or
> Label1.Caption=CStr(255 * CLng(255))
>
> Note: the CStr is not required as VB will coerce the numeric
result to a
> string to put it into the caption; I just prefer to make all
data
> conversions explicit rather than relying on VB to guess what I
mean.
>
>
>

[Randy Birch]

VB, in calculating the results to assign to x, uses a temporary variable. In
doing so, it creates and uses an internal temporary working variable whose
data type is the smallest possible one that would could contain without
error either of the values being multiplied.

In your case, because the both data types being multiplied are integers, VB
uses an integer as the temporary working variable. As the result of the
multiplication exceeds 32k (the limit for an integer), VB is forced to toss
an overflow error (even though VB itself was responsible for creating the
error in the first place!)

To ensure that VB will use an internal temporary working variable of a data
type sufficient to hold the result (as opposed to each item), you must
assign a type-declaration character to one of the values in the expression.
This, following the rules stated above, forces VB to use an internal
temporary working variable of sufficient capability to hold the result, thus
completing the action without error. For example:

x = 33 * 1000&

x will hold the correct result, since the expression indicated that 1000 was
to be treated as a Long (even though the value 1000 fits inside an integer)
and thus VB used a long to create its internal temporary working variable.
However, be aware that the code:

x = 33 * 1000 * 100&

will still generate the error. In this case, despite the inclusion of the
Long declaration character in the expression, VB must perform the
calculation in parts. Since the expression did not contain brackets forcing
one portion to be evaluated over another, VB attempts to compute the first
part of the multiplication ( 33 * 1000 ) into its internal temporary working
variable created it as an integer, again generating the error.

The fix under these circumstances is, as above, to assign the long to the
one of the first two values being evaluated largest value, or to bracket the
equation to have VB perform the computation containing the long first:

x = 33 * 1000& * 100
x = 33 * (1000 * 100&)


--

Randy Birch
MVP Visual Basic
http://www.mvps.org/vbnet/
Please respond only to the newsgroups so all can benefit.


"Miroslav St. Jeliaskoff" <miroslav@earthling.net> wrote in message
news:3d305378$1@10.1.10.29...
> Why I can't get this result?
>
> Label1.Capton = 255 * 255
>
> Isn't it strange? Atleast for me it is!
>
> Miroslav St. Jeliaskoff
>
>