When to use classes?

[shaggy]

Hey everyone, I have been learning c++ for around 1 year, but i am still not very good. I programming in an object oriented manner, but would just like some advice.

If i was to make a console RPG where there were different character you could be(wizard, warrior etc.) , when and where would i use a class?

And if I am making a Contact manager to add, delete and save contacts and their name, what kind of OOP related coding should i have. And by 'should' i mean what is the most neccarsary and effeciant way to code and make the programm.

THankyou verymuch :)

[Aceix]

OP wrote:

And if I am making a Contact manager to add, delete and save contacts and their name, what kind of OOP related coding should i have.

Maybe you could make a class with functions(of cause virtual for OOP) and the "database" then a derived class would make its implementation of these functions.....of that sought.

[shaggy]

Oh i see, thanks man.
One thing, I am just wondering what implementation means in that context ("a derived class would make its implementation of these functions")?

Well, basically i am wondering what implementation means in OOP in general. thanks:)

[Aceix]

Resource: http://uk.answers.yahoo.com/question/index?qid=20081019073402AAdZHTc

As a general term, implementation is the actual code that has been created based on a hypothetical design, so to implement a program is to actually program it.

In object-oriented programming, two terms are "interface" and "implementation." The interface is akin to the blueprint of an object or a system. It shows the methods, variables, documentation about a class. The implementation is how it actually works (e.g., the workflow, code, etc.)

Here's a very short, elementary example:

//Car interface in file car.h
class Car
{
public:
Car()
~Car()
Accelerate()
Decelerate()
private:
int speed;
};

This is the interface. It's what programmers will see when they use the car class.

Now, the IMPLEMENTATION (which actually fleshes out the methods)

//in car.cpp

void Car::Accelerate()
{
speed++;
}

void Car::Decelerate()
{
speed--;
}

[shaggy]

Oh great, thankyou, Aceix. THanks for replying, no one usually replies to my threads anymore, i dont know why. I made one juts before, which got no replies.

Anyway just to clarify, does the implementation simply mean the member functions of a class and how they operate and use the class?

So when you said: "then a derived class would make its implementation", you meant a derived class that would use the functions of the other class?

And what is a dervied class? thanks man

[Aceix]

What I know is, implementation/definition" of a virtual function of a base class, is to give a version of that function.

a base class, is a class that other classes inherit from.
and a derived class is a class, which inherits from a base class.

Note: private methods(functions) or variables cannot be inherited, but can be accessed, by friend classes and functions.

Sounds confusing, look at this:

class Polygon  //which is a base class.
{
     public:
      virtual int area(int,int){};    //a virtual function the reason for the {} is to give some implementation or else you'll get some 'vtable' error.
// Note this applies to virtual methods and not pure virtual ones.
};

class square:public Polygon{
     int area(int a, int b){return a*b;}   //its version of the virtual function.
//Note. parameters and return type, and also the name of the function, must be the same!
};

class triangle:public Polygon{
     int area(int a,int b){return (a*b/2);} //its version too
}

For more info: http://cplusplus.com/doc/tutorial/inheritance/
and http://cplusplus.com/doc/tutorial/polymorphism/

[shaggy]

Oh thanks alot man. So, if it were an rpg, would i make a base class for 'Player' and have all of the different type of players(wizard, warrior etc.) as child classes coming off the base class ?

Is it common to do that all of the time in these scenarios? Like If i had a car, then the different types of car would be coming off a base class?

THanks again man:)

[Aceix]

OP wrote:

Is it common to do that all of the time in these scenarios? Like If i had a car, then the different types of car would be coming off a base class?

Yeah like this. All cars have mass(since it is matter) and a type(SUV,convertible,...). So you can have a base class with weight(); function and type(); then a derived class say Lamborghini Murcielago would implement it...that sort since now you understand........

Thanks for the replies. They make me active in forums!

[shaggy]

Thanks alot man, you've been a great help. Thanks for replying. I'll just go learn and practice everything you said :) bye