On Wed, 16 Apr 2008 16:57:04 -0500 (CDT) in comp.lang.c.moderated,
Philluminati <Phillip.Ross.Taylor@[EMAIL PROTECTED]
> wrote:
>I am writing a poker game which needs to work with cash. I am aware
>that there are problems with floats that make them unsuitable for
>storing money values. On top of this I may be expected to do
>operations such as =A310.52 / 3. Which data type should I use instea=
d?=20
Most code uses double, some with careful attention to rounding.=20
Some code uses scaled integers stored in double and used only in thei=
r
exact integer range, with careful attention to rounding.=20
Some code may use scaled long or long long int, with careful attentio=
n
to rounding.=20
Look for info on guard digits and rounding.=20
>Is there an Industry standard one?
Packed Decimal or Binary Coded Decimal strings which are not sup****te=
d
in C. Mike Cowlishaw has a library for decimal character digit string=
s
in C: http://www2.hursley.ibm.com/decimal/#decNumber.=20
>Further to this, is anyone away of legally what the obligations woul=
d
>be when the outcome is 3.566666667? does the customer get 56 or 57p=
?
Look for info on bankers' rounding.=20
>Do I need to track the remaining .003333 and use it in other
>operations?
You may have to store higher precision than you output: look for info=
on
rounding.=20
>And finally, why do I see people typedef values in C and, for exampl=
e,
>use size_t rather than an int? Why is the type hidden like this?
****tability: standard compliant compiler implementors have to provide
certain types, as they are required by the standard, and so may safel=
y
be used by ****table programs to do the right thing on multiple
platforms.=20
Certain platform standards like POSIX also specify additional types a=
nd
functions that may be available in your compiler's headers and librar=
ies
and useful in interfacing to the platform.=20
>Surely it can lead to bugs and changing a data type later in
>development can allow bitwise and maths operations to become un-
>trustable?=20
Programmer defined datatypes sup****t abstraction, which allows the
programmer to change the data definitions and sup****ting functions
without changing or even recompiling source code elsewhere, which may
involve hundreds of source modules containing megabytes of code.=20
Data and module structuring and organization is one of the hardest
lessons to learn in programming and not written about a lot.=20
Since structured programming has given way to object oriented (in som=
e
opinions, unstructured) and Pascal has become less popular, coverage =
of
programming principles e.g. in books by Wirth and papers by Dijkstra
have been neglected, although Hunt & Thomas' The Pragmatic Programmer=
,
Kernighan & Pike's The Principles of Programming, and Joel Spolsky's
collections of articles have appeared fairly recently and may still b=
e
available in some larger or technical stores. Diomedis Spinellis is a=
lso
writing an O'Reilly series on Code: Reading, Quality, ...=20
If you keep the highest compiler warning levels enabled, a compiler m=
ay
be able to tell you if operations will/may fail.=20
Choice of suitable data representations and operations keeping values
used (including tem****ary intermediates) within their valid ranges is
the ultimate responsibility of the programmer.=20
>In my own applications I have been typdef'ing structures
>merely to remove the requirement to write "struct" everywhere and I
>see how shortening the name of unsigned long to ulng would be useful
>but I don't see it's benefit in some cases. So why do people use it?
IMHO laziness: to avoid some typing at the expense of some clarity.=
=20
>I'm sorry if these questions seem stupid or simple but I'm new to C
>and I can't find that many resources for C.
The monthly FAQ postings in this group may give you more background a=
nd
references.=20
The C Standard Rationale is freely downloadable, and may explain why
certain decisions were made, although you may not understand all of i=
t
yet.=20
Books like K&R2, Harbison & Steele, Plauger's the Standard C Library =
or
anything by him, Oualline's C Elements of Style, Holub's Enough Rope =
to
Shoot Yourself in the Foot, Heathfield Kirby et al's C Unleashed, and
others recommended in the ACCU booklist below give more background,
info, and examples, and should be available thru a technical library =
or
inter-library loan.=20
http://accu.org/index.php/book_reviews?url=3Dsearch.xqy%3Fx&term=3Dbe=
ginner+AND+C&field=3Dbody
--=20
Thanks. Take care, Brian Inglis =09Calgary, Alberta, Canada
Brian.Inglis@[EMAIL PROTECTED]
=09(Brian[dot]Inglis{at}SystematicSW[dot]ab[dot]=
ca)
fake address=09=09use address above to reply
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