Classes

[arganx]

I'm new. All of my books when talking about classes always use some
sort of "database" example, e.g. tracking stock, tracking baseball
stats, etc.

I'm trying to think OOP and wonder is there are uses for classes for ME
to use within my program. In other words a class of ? to help me to do
?. I can't see that this would be different than a function, or am I
completely missing it.

Any comments, ideas or short examples would be appreciated.

[Greg Comeau]

In article <11**********************@g47g2000cwa.googlegroups .com>,
arganx <ar*******@yahoo.com> wrote:

I'm new. All of my books when talking about classes always use some
sort of "database" example, e.g. tracking stock, tracking baseball
stats, etc.

I'm trying to think OOP and wonder is there are uses for classes for ME
to use within my program. In other words a class of ? to help me to do
?. I can't see that this would be different than a function, or am I
completely missing it.

Any comments, ideas or short examples would be appreciated.

In many cases you actually _do_ just want a function.
Note that that focuses often on solely an perspective
that is algorithmic, simple, and perhaps only a uni-operation.
Classes tend to focus on types, subsystems, and relationships
up and down related types, along with their usually
multiple operations. The question isn't solely just
can't I just use functions to code up my problems,
because obviously computer languages have been around
for a while, and people have been able to provide fairly
elaborate applications even though those lanuages did not
directly support OOP. The issue is more of how we can break
down problems, spell out the interaction and operations
which need to occur, and best design and model the task at hand.

Unfortunately, we cannot do your question justice in a NG, however,
I know you express what many folks wonder, and go through.
For well thought out ideas, etc I would suggest getting
the below two books in addition to your current ones.

I would get Stroustrup's The C++ Programming Language
(3rd or special edition) and have a look at Chapter 2, 1,
23, 24, 25. These are issues pretty much never ever discussed
in many so-called beginner [C++] books, and yet they are
exactly about what most of it's all about. It's ok if
you don't get everything on your first read because you
will have this book for a long time. Better yet, get
two copies and wallpaper the room with it.

Similarly, get Koenig and Moo's Accelerated C++. It tends
to reverse the normal introductory progression from the
random low-level hen-pecking solutions looking for problems
approach and throws you right into what it's all about
such as abstraction, problem solving, class design, etc.

These two texts are authoritative, to the point, insightful,
and then some. Neither is particularly an easy read for
everybody, however, they are spot on where you need to be.

See http://www.comeaucomputing.com/booklist for isbn info, etc.
--
Greg Comeau / Celebrating 20 years of Comeauity!
Comeau C/C++ ONLINE ==> http://www.comeaucomputing.com/tryitout
World Class Compilers: Breathtaking C++, Amazing C99, Fabulous C90.
Comeau C/C++ with Dinkumware's Libraries... Have you tried it?

[osmium]

"arganx" writes:

I'm new. All of my books when talking about classes always use some
sort of "database" example, e.g. tracking stock, tracking baseball
stats, etc.

I'm trying to think OOP and wonder is there are uses for classes for ME
to use within my program. In other words a class of ? to help me to do
?. I can't see that this would be different than a function, or am I
completely missing it.

Any comments, ideas or short examples would be appreciated.

That is, indeed, a significant problem It might help if we knew what field
you were in. If you are an old-timey programmer, think of a stack, a linked
list, a tree, a string as a nice repository of handy tools you can pick up
and use.

A person who writes simulators could have a random number class that
provides, a bunch of different distributions. Uniform, Gaussian, Poisson,
.... and a selection of generators of varying qualities.

If you are into statistics, you could have classes that do some of the
common things, standard deviation, chi-square, ... in classes.

If you are into math you could have a matrix class. And of course, most
everyone in any of the sciences can use the complex class, which is, more or
less, built in, to C++.

I would think an architect could use a window (NOT tm) class, a door class,
an elevator class.

Another approach, it may be helpful to think of a class as a mini program
with a, possibly, very rich interface.

[osmium]

"osmium" wrote:

<snippage>

That is, indeed, a significant problem It might help if we knew what
field you were in. If you are an old-timey programmer, think of a stack,
a linked list, a tree, a string as a nice repository of handy tools you
can pick up and use.

One thing I forgot to mention. There are a lot of people who will go to
great lengths to use classes, even when, IMO, the payback is actually
negative. I think OOP has been grossly oversold, and I wish someone had told
me that many years ago. I had to figure it out for myself.

The attitude of many seems to be "I have this great new hammer and I'll be
damned if I am going to let it just rust away in the toolbox...." OOP and
classes are far from a silver bullet.

[Ben Pope]

arganx wrote:

I'm new. All of my books when talking about classes always use some
sort of "database" example, e.g. tracking stock, tracking baseball
stats, etc.

I'm trying to think OOP and wonder is there are uses for classes for ME
to use within my program. In other words a class of ? to help me to do
?. I can't see that this would be different than a function, or am I
completely missing it.

Any comments, ideas or short examples would be appreciated.

Don't think of "objects" as physical objects. Often, it is ideal, but
often it will lead you astray.

A class is used to encapsulate some data along with operations on that
data. You can use it to abstract the implementation of a concept; that
concept could be anything, but usually it involves state (stored in the
data, and operated on by the methods).

As you gain experience with programming you will (hopefully!) learn to
think in terms of abstractions of concepts - the rest is relatively easy.

Ben Pope

[arganx]

Thank you all for your comments. It has given me ideas to think about
and other references to study.

[Eric Chomko]

osmium (r1********@comcast.net) wrote:
: "osmium" wrote:

: <snippage>

: > That is, indeed, a significant problem It might help if we knew what
: > field you were in. If you are an old-timey programmer, think of a stack,
: > a linked list, a tree, a string as a nice repository of handy tools you
: > can pick up and use.

: One thing I forgot to mention. There are a lot of people who will go to
: great lengths to use classes, even when, IMO, the payback is actually
: negative. I think OOP has been grossly oversold, and I wish someone had told
: me that many years ago. I had to figure it out for myself.

I agree. I was taught top-down structured programming (Dijkstra et. al.)
25-30 years ago and have had a difficult time re-thinking in OOP.
Object-oriented design is fine, but my OOP tends to go back to the old way
of thinking to the point I said the heck with it.

I think if you can come up with (a) data structure(s) that can handle your
application, then the code will come out of that (i.e. think data first
and code second and your OO approach tends to fall into place).

: The attitude of many seems to be "I have this great new hammer and I'll be
: damned if I am going to let it just rust away in the toolbox...." OOP and
: classes are far from a silver bullet.

Agreed.

Eric