Superclass and Subclasses

[Marko]

I have abstract superclass named Element, and several subclasses
derived from it: And, Or, Nand, Nor...
I have method which has to take 2 subclasses of element as its
parameters types.
Can't use void myFunction(Elem ent& e1,Element& e2); prototype because
I am trying to pass it objects of class And or any other subclass.
Need help..

[Marko]

On Sep 1, 5:50 pm, Erik Wikström <Erik-wikst...@telia. comwrote:

On 2007-09-01 17:42, Marko wrote:

On Sep 1, 5:34 pm, Rolf Magnus <[e-mail]:

Marko wrote:
On Sep 1, 12:38 pm, Neelesh Bodas <neelesh.bo...@ gmail.comwrote:
On Sep 1, 3:22 pm, Marko <cb...@outgun.c omwrote:

I have abstract superclass named Element, and several subclasses
derived from it: And, Or, Nand, Nor...
I have method which has to take 2 subclasses of element as its
parameters types.
Can't use void myFunction(Elem ent& e1,Element& e2); prototype because
I am trying to pass it objects of class And or any other subclass.
Need help..

Why can't you use void myFunction(Elem ent& e1,Element& e2); ? If
'And', 'Or' etc are publicly derived from Element then 'And' is-an
'Element' and hence it can be passed to a function which exepcts an
Element&. What is the exact issue?

-N

OK, it just start working.
I don't know what happened. I probably overlooked something obvious.

But now, I have new problem, and this time I'm not even sure that this
thing
can be done the way I am trying to do it.

I have to make a dynamic array of Element type, so it can contain any
of the derived class objects.

You cannot make an array of that kind. But you can make an array of pointers
to Element, and those can point to derived class objects.

You mean somthing like Element** myArray;?

Yes, or Element* myArray[size], or even better std::vector<Ele ment*>.

--
Erik Wikström

Actually, the thing is I have to compose another class that is derived
from Element called Circuit.
Circuit has dynamic array of Elements as member. Pain..

Now, I declared Element* element; in Circuit
and made a constructor for Circuit which has int n as parameter.
It looks something like this:

class Circuit: public Element{
public:
Circuit(char name...int n):Element(name ,...){elements= new
Element[n]}
~Circuit(){dele te []elements;}

Element* elements;

//some overloaded functions of Element...
};

compiler says something like: no appropriate default constructions
available

[Marko]

On Sep 1, 6:15 pm, Marko <cb...@outgun.c omwrote:

On Sep 1, 5:50 pm, Erik Wikström <Erik-wikst...@telia. comwrote:

On 2007-09-01 17:42, Marko wrote:

On Sep 1, 5:34 pm, Rolf Magnus <[e-mail]:
>Marko wrote:
On Sep 1, 12:38 pm, Neelesh Bodas <neelesh.bo...@ gmail.comwrote:
>On Sep 1, 3:22 pm, Marko <cb...@outgun.c omwrote:

I have abstract superclass named Element, and several subclasses
derived from it: And, Or, Nand, Nor...
I have method which has to take 2 subclasses of element as its
parameters types.
Can't use void myFunction(Elem ent& e1,Element& e2); prototype because
I am trying to pass it objects of class And or any other subclass.
Need help..

>Why can't you use void myFunction(Elem ent& e1,Element& e2); ? If
>'And', 'Or' etc are publicly derived from Element then 'And' is-an
>'Element' and hence it can be passed to a function which exepcts an
>Element&. What is the exact issue?

>-N

OK, it just start working.
I don't know what happened. I probably overlooked something obvious.

But now, I have new problem, and this time I'm not even sure that this
thing
can be done the way I am trying to do it.

I have to make a dynamic array of Element type, so it can contain any
of the derived class objects.

>You cannot make an array of that kind. But you can make an array of pointers
>to Element, and those can point to derived class objects.

You mean somthing like Element** myArray;?

Yes, or Element* myArray[size], or even better std::vector<Ele ment*>.

--
Erik Wikström

Actually, the thing is I have to compose another class that is derived
from Element called Circuit.
Circuit has dynamic array of Elements as member. Pain..

Now, I declared Element* element; in Circuit
and made a constructor for Circuit which has int n as parameter.
It looks something like this:

class Circuit: public Element{
public:
Circuit(char name...int n):Element(name ,...){elements= new
Element[n]}
~Circuit(){dele te []elements;}

Element* elements;

//some overloaded functions of Element...

};

compiler says something like: no appropriate default constructions
available

Perhaps i could use linked list of elements? Would that change
anything?

[=?ISO-8859-1?Q?Erik_Wikstr=F6m?=]

On 2007-09-01 18:53, Marko wrote:

On Sep 1, 6:15 pm, Marko <cb...@outgun.c omwrote:

>On Sep 1, 5:50 pm, Erik Wikström <Erik-wikst...@telia. comwrote:

On 2007-09-01 17:42, Marko wrote:

On Sep 1, 5:34 pm, Rolf Magnus <[e-mail]:
Marko wrote:
On Sep 1, 12:38 pm, Neelesh Bodas <neelesh.bo...@ gmail.comwrote:
On Sep 1, 3:22 pm, Marko <cb...@outgun.c omwrote:

I have abstract superclass named Element, and several subclasses
derived from it: And, Or, Nand, Nor...
I have method which has to take 2 subclasses of element as its
parameters types.
Can't use void myFunction(Elem ent& e1,Element& e2); prototype because
I am trying to pass it objects of class And or any other subclass.
Need help..

>Why can't you use void myFunction(Elem ent& e1,Element& e2); ? If
'And', 'Or' etc are publicly derived from Element then 'And' is-an
'Element' and hence it can be passed to a function which exepcts an
Element&. What is the exact issue?

>-N

OK, it just start working.
I don't know what happened. I probably overlooked something obvious.

But now, I have new problem, and this time I'm not even sure that this
thing
can be done the way I am trying to do it.

I have to make a dynamic array of Element type, so it can contain any
of the derived class objects.

>You cannot make an array of that kind. But you can make an array of pointers
to Element, and those can point to derived class objects.

You mean somthing like Element** myArray;?

Yes, or Element* myArray[size], or even better std::vector<Ele ment*>.

--
Erik Wikström

Actually, the thing is I have to compose another class that is derived
from Element called Circuit.
Circuit has dynamic array of Elements as member. Pain..

Now, I declared Element* element; in Circuit
and made a constructor for Circuit which has int n as parameter.
It looks something like this:

class Circuit: public Element{
public:
Circuit(char name...int n):Element(name ,...){elements= new
Element[n]}
~Circuit(){dele te []elements;}

Element* elements;

//some overloaded functions of Element...

};

compiler says something like: no appropriate default constructions
available

It's because you created an array of Elements, you need pointers to Element.

Perhaps i could use linked list of elements? Would that change
anything?

No, but that does not mean you shouldn't use it (but a vector would be
even better), anything is better than a raw array. Remember this next
time you need to store some objects: when in doubt, use a vector.

--
Erik Wikström

[Marko]

On Sep 1, 7:32 pm, Erik Wikström <Erik-wikst...@telia. comwrote:

On 2007-09-01 18:53, Marko wrote:

On Sep 1, 6:15 pm, Marko <cb...@outgun.c omwrote:

On Sep 1, 5:50 pm, Erik Wikström <Erik-wikst...@telia. comwrote:

On 2007-09-01 17:42, Marko wrote:

On Sep 1, 5:34 pm, Rolf Magnus <[e-mail]:
>Marko wrote:
On Sep 1, 12:38 pm, Neelesh Bodas <neelesh.bo...@ gmail.comwrote:
>On Sep 1, 3:22 pm, Marko <cb...@outgun.c omwrote:

I have abstract superclass named Element, and several subclasses
derived from it: And, Or, Nand, Nor...
I have method which has to take 2 subclasses of element as its
parameters types.
Can't use void myFunction(Elem ent& e1,Element& e2); prototype because
I am trying to pass it objects of class And or any other subclass.
Need help..

>Why can't you use void myFunction(Elem ent& e1,Element& e2); ? If
>'And', 'Or' etc are publicly derived from Element then 'And' is-an
>'Element' and hence it can be passed to a function which exepcts an
>Element&. What is the exact issue?

>-N

OK, it just start working.
I don't know what happened. I probably overlooked something obvious.

But now, I have new problem, and this time I'm not even sure that this
thing
can be done the way I am trying to do it.

I have to make a dynamic array of Element type, so it can contain any
of the derived class objects.

>You cannot make an array of that kind. But you can make an array of pointers
>to Element, and those can point to derived class objects.

You mean somthing like Element** myArray;?

Yes, or Element* myArray[size], or even better std::vector<Ele ment*>.

--
Erik Wikström

Actually, the thing is I have to compose another class that is derived
from Element called Circuit.
Circuit has dynamic array of Elements as member. Pain..

Now, I declared Element* element; in Circuit
and made a constructor for Circuit which has int n as parameter.
It looks something like this:

class Circuit: public Element{
public:
Circuit(char name...int n):Element(name ,...){elements= new
Element[n]}
~Circuit(){dele te []elements;}

Element* elements;

//some overloaded functions of Element...

};

compiler says something like: no appropriate default constructions
available

It's because you created an array of Elements, you need pointers to Element.

Perhaps i could use linked list of elements? Would that change
anything?

No, but that does not mean you shouldn't use it (but a vector would be
even better), anything is better than a raw array. Remember this next
time you need to store some objects: when in doubt, use a vector.

--
Erik Wikström

So, how should it look?
Something like vector<Element* elements; instead of Element**
elements;?
And how do I load pointers to objects into it?

[Marko]

On Sep 1, 8:42 pm, Marko <cb...@outgun.c omwrote:

On Sep 1, 7:32 pm, Erik Wikström <Erik-wikst...@telia. comwrote:

On 2007-09-01 18:53, Marko wrote:

On Sep 1, 6:15 pm, Marko <cb...@outgun.c omwrote:
>On Sep 1, 5:50 pm, Erik Wikström <Erik-wikst...@telia. comwrote:

On 2007-09-01 17:42, Marko wrote:

On Sep 1, 5:34 pm, Rolf Magnus <[e-mail]:
>Marko wrote:
On Sep 1, 12:38 pm, Neelesh Bodas <neelesh.bo...@ gmail.comwrote:
>On Sep 1, 3:22 pm, Marko <cb...@outgun.c omwrote:

I have abstract superclass named Element, and several subclasses
derived from it: And, Or, Nand, Nor...
I have method which has to take 2 subclasses of element asits
parameters types.
Can't use void myFunction(Elem ent& e1,Element& e2); prototype because
I am trying to pass it objects of class And or any other subclass.
Need help..

>Why can't you use void myFunction(Elem ent& e1,Element& e2); ? If
>'And', 'Or' etc are publicly derived from Element then 'And'is-an
>'Element' and hence it can be passed to a function which exepcts an
>Element&. What is the exact issue?

>-N

OK, it just start working.
I don't know what happened. I probably overlooked something obvious.

But now, I have new problem, and this time I'm not even sure that this
thing
can be done the way I am trying to do it.

I have to make a dynamic array of Element type, so it can contain any
of the derived class objects.

>You cannot make an array of that kind. But you can make an array of pointers
>to Element, and those can point to derived class objects.

You mean somthing like Element** myArray;?

Yes, or Element* myArray[size], or even better std::vector<Ele ment*>.

--
Erik Wikström

>Actually, the thing is I have to compose another class that is derived
>from Element called Circuit.
>Circuit has dynamic array of Elements as member. Pain..

>Now, I declared Element* element; in Circuit
>and made a constructor for Circuit which has int n as parameter.
>It looks something like this:

>class Circuit: public Element{
>public:
> Circuit(char name...int n):Element(name ,...){elements= new
>Element[n]}
> ~Circuit(){dele te []elements;}

> Element* elements;

> //some overloaded functions of Element...

>};

>compiler says something like: no appropriate default constructions
>available

It's because you created an array of Elements, you need pointers to Element.

Perhaps i could use linked list of elements? Would that change
anything?

No, but that does not mean you shouldn't use it (but a vector would be
even better), anything is better than a raw array. Remember this next
time you need to store some objects: when in doubt, use a vector.

--
Erik Wikström

So, how should it look?
Something like vector<Element* elements; instead of Element**
elements;?
And how do I load pointers to objects into it?

Got it! Never mind.
I am most grateful for your help and time.
As you can probably see I am pretty new at this. In fact, this is my
first contact with OO programing.
And also a school project :)
You've been most helpful.