objects and methods

For Beginners

Started by conejo5991 September 13, 2009 09:05 AM

16 comments, last by Frederick 14 years, 7 months ago

3,128

September 13, 2009 03:50 PM

Quote:Original post by conejo5991
cout>>, or cin>>, or if/else, or while/do, for/next

That kind of thing. All things algorithmic.

cout and cin are not 'primitive' nor are they 'types. They aren't primitive in the same way if/else and while/do are. None of those things are types either, 'int' and 'float' are types. Also, there is no 'next' in C++ so I'm not sure where you got that from. cout and cin are objects provided by the compiler vendor that allow the program to interact with a console. If you don't need to interact with the console you don't need cout or cin.

Quote:Once you get OOP going, the member function at least has these things right?

Many classes will use some or all of those things, but it's not really a requirement so much as a byproduct of how programming works. One thing that many programs don't actually use in the 'real world' is cout and cin. It's almost impossible to avoid ifs, whiles, and fors in a program though. An individual member function doesn't necessarily have to use any of that to work even if most will. It depends on what the member function does. Sometimes the member function will just do do some math or even just return data. It depends and it's not a good idea to make hard and fast 'rules' about what a program 'must' have.

Quote:But two or three replies ago, someone said that OBJECTS have only data. I was under the mistaken impression that OBJECTS have these primitive algorithmic types within them.

Is that true?

As you said in your original post "a member function is associated with an object". Associated is kind of a loose term, so in some sense an object could have 'algorithms in it', but that's generally not the most productive way to think about it. An object has data and associated member functions, but the member functions aren't really part of an object. They are however associated with all of the objects of that type(ie, the class) and the member functions operate on individual[i/] objects when invoked.

This concept can be further illustrated by comparing regular member functions to static member functions. Static member functions don't operate on an object they operate on all objects(ie, the class). As such a static member function can't modify member variables of individual objects(how would the program know which members to modify?), only static member variables which are shared between all objects. I wouldn't be surprised if that confuses you further if so I'm sorry.

All that aside, in many cases the distinction between 'an object is only data with associated member functions' and 'an object is data and member functions' won't really matter. But eventually you'll do something that won't make sense unless you remember that there is one set of code shared by multiple sets of data.

Quote:And by the way, is there such a thing online as a simple C++ OOP course, maybe even free, but you can't expect too much I guess, where the instructor could possibly clear all these things up for me, and then I could really get a jumpstart on coding?

There's not really any place where someone will work with you one-on-one. But if you have further questions you can ask here. The closest thing I can think of to what you want is right here at gamedev in the "CPP Workshop" forum. The concept was to have a workshop where everyone would follow along in the same book and post questions and get answers. You can post a question, but you might not get answer for awhile as there isn't heavy traffic there any more. However, there's a good chance someone has already had the same questions as you so you could just read the threads associated with a particular chapter for questions and answers other people had.

Hope this helps.

C++: A Dialog | C++0x Features: Part1 (lambdas, auto, static_assert) , Part 2 (rvalue references) , Part 3 (decltype) | Write Games | Fix Your Timestep!

conejo5991

100

Author

September 13, 2009 03:51 PM

But data can contain what used to be considered line commands.
Is that correct?
Isn't it true, then, in a nutshell,
that the class declares, the object puts forth
the arguments, and the methods do most of
the mathematics?
Of course, unless you use a void function
where it does what an object would do,
but for some reason is an extra subroutine?

better living throughprogramming

conejo5991

100

Author

September 13, 2009 04:10 PM

I don't disagree with your concept of non OOP statements
because eventually the teacher I had said to tle class
that what we thought were line commands were actually
kinds of variables, or as you say, classes.
True, but my problem or point of view is that
most of the programming I did years ago
was with what they used to call line commands
in early 80's BASIC, with line numbers even.
What a trip. But now I see it as algorithmic programming,
and I have to get comfortable with OOP.

I'm not trying to be confusing or anything,
but I see the object as something similar to
what I USED TO call line commands,
although even I have been shown that ultimately
they are not. It just helps me in my conceptualization
at this point so I can get this clear picture I need.
Call it stubborness if you will.
I also have a creative side, which you probably do too
if you can write in OOP.

On the other hand, is there a book you know of
that makes all these terms really clear,
maybe even written for kids.
And has really simple broken down examples
and enlightening projects?
Because to be honest with you,
I do much much better when I study math,
science, and even programming,
with layman's books. I'm just not good with
technical terms even though my vocabulary is fairly decent.

better living throughprogramming

nullsquared

128

September 13, 2009 04:42 PM

Can you please stop
writing like this?
I really want to help you
but I can't bring myself
to read whatever you're
writing because it's really
annoyingly layed out.

www.nullular.com

conejo5991

100

Author

September 13, 2009 05:11 PM

Dear Nullsquared, If you could get me to understand my problem with how an method is associated with an object, then, of course I will do my best to change my wording schema. Could you then put forth for me, the appropriate framework into which I should alter my questioning schemata? Right now I don't have a framework other than that which comes forth in an intuitional manner
which seems to me to be in conformity to a move from algorithmic thinking into a more OOP frame of mind, because I have even myself noticed that some of the questions I post, and I have posted other places, will actually cause me to be enlightened toward to resolution of this matter, even though I only considered it to be a question. But when I write out the thought process in a question form of statement, then the rereading of it, or merely considering of it, will actually bring some kind of enlighenment towards the full resolution of the problem, of which I must be ignorant, otherwise I would not pose the question in gthe first place. So it seems to me that I am making my best attempt to move forward positively on the ignorance-enlightenment continuum.
But seriously, and I wasn't trying to be too unserious previously,
If you can give me a more organized way to put forth a question, to which I don't yet have an answer, which can help other programmers who are reading my question and trying to help me, to better understand even what I am trying to actually say, then most assuredly, I will do my best to follow such a path.
I guess this has something to do with why my high school English papers didn't get thde best of grades, even though I spent hours writing them.
So, even your response to this reply could actually move me towards getting better in language expression, which could go even further than programming skills by themselves.

better living throughprogramming

DevFred

840

September 13, 2009 05:27 PM

Quote:Original post by conejo5991
But data can contain what used to be considered line commands.
Is that correct?
Isn't it true, then, in a nutshell,
that the class declares, the object puts forth
the arguments, and the methods do most of
the mathematics?
Of course, unless you use a void function
where it does what an object would do,
but for some reason is an extra subroutine?

I'm sorry to say this, but I have absolutely no idea what you are talking about. Maybe you should just grab a beginner's C++ book and start programming. I suggest "Programming: Principles and Practice using C++" and "C++ Primer" and "Accelerated C++". Pick any of these and start.

nobodynews

3,128

September 13, 2009 06:25 PM

I'll give it one last shot at trying to explain. To the compiler these two programs are effectively identical:

#include <iostream>struct Foo{    int x;};void SetFooX(Foo * foo, int newX){    foo->x = newX;}int SquareFooX(Foo * foo){    // assume foo is a valid pointer    return foo->x * foo->x;};int main(){    Foo foo;    SetFooX(&foo, 5);    int x = SquareFoox(&foo);    std::cout << "foo.x^2 == " << x << std::endl;}

#include <iostream>class Foo{    int x;public:    void SetFooX(int newX)    {        x = newX;    }    int SquareFooX()    {        return x * x;    }};int main(){    Foo foo;    foo.SetFooX(5);    int x = foo.SquareFooX();    std::cout << "foo.x^2 == " << x << std::endl;}

You wouldn't say that in the first example that the struct Foo has the functions SquareFooX and SetFooX. In fact, in back-in-the-day C++, C++ compilers just converted the 2nd source code into the 1st source code and then used a C compiler on the converted code.

And while I'm rereading your original post, I see you asked for a 'bonehead example of an object interacting with a member function'. See this line?

foo.SetFooX(5);

SetFooX is the member function interacting with the object foo.

As for your other question, you can't make the member function user defined in C++. That all happens before you compile. If you want that functionality in C++ you're in for a world of hurt because it doesn't exist. This is why people use languages that support reflection when they want this. As you can see in the examples C++ is not listed. If you want reflection in C++ you basically need to embed a scripting language into your program. At this stage in you're learning I suggest you forget about it.

C++: A Dialog | C++0x Features: Part1 (lambdas, auto, static_assert) , Part 2 (rvalue references) , Part 3 (decltype) | Write Games | Fix Your Timestep!

Frederick

140

September 13, 2009 07:03 PM

Hi conjeno,

sorry didn´t follow the thread as a whole, but what i understood is, that you are greatly confused. It seems you are approaching the whole subject too technically.

Object oriented programming is an approach to make programming more intuitive for human programmers. In everyday life you deal with objects all the time. Objects may be trees, cars, animals, people whatever. Objects have particular properties,
like smell, color, sound etc. This is conceptual the same as the programming term "object property" or "object variable".
Particular objects are also able to perform actions like humans and animals and machines. When an object performs an action, the state of the world may be changed, the object may either affect itself or any other object. You may
understand actions as the programming term "method". A method is a sequence
of actions to achieve a certain goal in the world and in achieving that goal
may affect other objects. If you would like to still your hunger, a method would be to cook, or go to McDonalds.

An object performs an action, when you ask it to do so. You send the object a message. If you have an object of type "car" you could send it different messages like car->turnEngines(On/off); car->steerWheel(left/right);
The important point is, that it has an easy intuitive interface to the outside,
but is complicated in the inside. The car has subobjects, such as wheels, the engine an electric system. But it is completely hidden by a simple interface.
That is what makes OOP so powerful. Also it divides your project into dozens of different objects, which may each be understood by its own, instead of one big mess of a program.

Last but not least you may asked, what classes are for. These are out of everyday usage also. Say you have red, a blue and a green pencil. It is the same concept "pencil" regardless the color. You would only introduce one class in your program to model this - a class called "pencil" with an attribute or property "color". You may now instance this concept into arbitray indivudal objects without repeating yourself over and over again. You don´t need to mention the shape and the function of the pencil again, just its particular attributes.

Hope this helps a bit. This is by no means complete, just a quick flow of my mind to get you a bit on track. Sorry, i can´t write more. My advise is don´t think too technically ;-)

Cheers,
Frederick

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