Class Arrays

This is a discussion on Class Arrays within the C++ Programming forums, part of the General Programming Boards category; I was wondering how you can define an array of the same class. Pretend we have 10 different cars and ...

  1. #1
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    Class Arrays

    I was wondering how you can define an array of the same class. Pretend we have 10 different cars and they all have the same properties. (This isn't really what I'm doing, but just a made up example).

    Code:
    class Car
    {
    public:
    	unsigned int year;
    	unsigned char color[256];
    	unsigned short weight;
    }
    Now say I want to create multiple instances of Car class in an array. Would I do something like this?:

    Code:
    Car cars[10];
    If this is correct, could I do something like this to loop through and get information from a user? Just an example:
    Code:
    	for( unsigned int i = 0; i < 10; i++ )
    	{
    		cout << "Enter a cars year: \n";
    		cin >> cars[i].year;
    		cout << "Enter a cars color: \n";
    		cin >> cars[i].color;
    		cout << "Enter a cars weight: \n";
    		cin >> cars[i].weight;
    	}
    	
    	for( unsigned int i = 0; i < 10; i++ )
    	{
    		cout << "Year: " << cars[i].year;
    		cout << "\tColor: " << cars[i].color;
    		cout << "\tWeight: \n" << cars[i].weight;
    	}

  2. #2
    C++まいる!Cをこわせ! Elysia's Avatar
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    Indeed, you could. Your example is correct.
    You just beware that you're destroying the entire purpose of the class. This isn't a class, this is a POD.
    Classes hide the implementation. Just so you're aware.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.
    For information on how to enable C++11 on your compiler, look here.
    よく聞くがいい!私は天才だからね! ^_^

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    Awesome! Guess I'll just have to play around with it.

    Can you elaborate on POD's and how I'm destroying the purpose of the class? Not sure what you mean, I am still new to this class thing.

  4. #4
    C++まいる!Cをこわせ! Elysia's Avatar
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    A class is like an object. If you make a car, you don't expose the car's internals.
    Instead, you expose a public interface, such as a wheel or pedestals for acceleration and retardation.
    These public interfaces then control the hidden engine and interfaces with all the other parts of the car, which you don't see.

    The same idea holds true for classes. It exposes a public interface (methods, functions), but hides its internals (variables). The methods manipulate the internal data in such a way that you, as a programmer that creates an instance of the class, do not have to worry about what goes on inside the class, only that the function do their work.

    A POD is essentially a struct with just members. No functions, no constructors, and all members are visible. It is treated as a separate type according to the standard. It's a POD.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.
    For information on how to enable C++11 on your compiler, look here.
    よく聞くがいい!私は天才だからね! ^_^

  5. #5
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    POD Type = Plain Old Data Type
    You could write the same thing as:
    Code:
    struct Car
    {
    	unsigned int year;
    	unsigned char color[256];
    	unsigned short weight;
    }
    In C++ a struct is the same as a class, except it defaults to public, whereas class defaults to private; but a lot of people use a struct instead of a class when they need a POD.

  6. #6

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    I'm a little bit confused... wouldn't a class with a member of itself be some infinitely recursive type?

    Code:
    struct Uh_Oh
    {
         struct Uh_Oh n;
    }    obj;
    
    obj.n.n.n.n ...

    EDIT:
    I just realized this didn't even happen in the code, so never mind.
    Last edited by rudyman; 06-23-2008 at 01:25 PM.

  7. #7
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    >> wouldn't a class with a member of itself be some infinitely recursive type?
    Yes, that is not allowed. But nobody is doing that here, are they?

  8. #8
    C++まいる!Cをこわせ! Elysia's Avatar
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    The code won't compile because Uh_Oh hasn't been declared at this point (or is in the process of being declared). But you can drop the "stuct" word:
    Code:
    struct Uh_Oh
    {
          Uh_Oh x;
    };
    In C++, we have a luxury C coders don't.
    (Or are you hijacking the thread with C code?)
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.
    For information on how to enable C++11 on your compiler, look here.
    よく聞くがいい!私は天才だからね! ^_^

  9. #9
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    That's not allowed either, Elysia. An Uh-Oh cannot contain an Uh_Oh.

  10. #10
    C++まいる!Cをこわせ! Elysia's Avatar
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    Well, no, I didn't say it was allowed, either.
    But the "static" keyword can be dropped, which was all I implied. It doesn't matter if it's there or not.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.
    For information on how to enable C++11 on your compiler, look here.
    よく聞くがいい!私は天才だからね! ^_^

  11. #11
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    Quote Originally Posted by Elysia View Post
    A class is like an object. If you make a car, you don't expose the car's internals.
    Instead, you expose a public interface, such as a wheel or pedestals for acceleration and retardation.
    Or better yet, add a drive() method so the user doesn't have to fiddle around with wheels and pedals, which may be replaced with trackballs and levers in the future.

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