sharing information in a class

[Dan]

Hello,

I have trouble with class calling. I am calling getvolume() with succes in
the function CreateCircle but it do not want to call it in ShowCircle()
function. I am staying in the same class. I thought that was the point of
encapsulation. When the function ShowCircle() is called I get very large
number -1.07374e+008
can anyone help me ?
class Circle
{
public:

Circle (int radius){
itsRadius = 0; }
void CreateCircle();
void ShowCircle();

void SetVolume( float radius){
volume = PI * pow(radius,2); }
float GetVolume(){ return volume; }

private:
float itsRadius;
float volume;
};
void Circle::CreateC ircle() //Draw a circle
{ char color;
float itsRadius, volume;

cout<<"Enter the radius in cm: " ;
cin>> itsRadius;

SetVolume(itsRa dius);
cout<<" Volume: " << GetVolume() <<endl;
}
void Circle::ShowCir cle()
{ int i;
cout <<" Volume is : " <<GetVolume() <<" cm cube " <<endl;
}

[Dan]

Where do you need it "outside"?

In ShowWidth() I want to get pConstRect->GetWidth() , but it do not
work, only in the function where pConstRect has been declared. I need it to
get this information in another function., This is the same problem as the
other problem with the radius..

#include <iostream>
#include <conio.h>
using namespace std;

class Rectangle
{
public:
Rectangle();
~Rectangle();
void SetLength(int length) { itsLength = length; }
int GetLength() const { return itsLength; }

void SetWidth(int width) { itsWidth = width; }
int GetWidth() const { return itsWidth; }

void ShowWidth();

private:
int itsLength;
int itsWidth;
};
Rectangle::Rect angle():
itsWidth(5),
itsLength(10)
{}
Rectangle::~Rec tangle()
{}

int main()
{
Rectangle* pRect = new Rectangle;
const Rectangle * pConstRect = new Rectangle;

cout << "pConstRect width: " << pConstRect->GetWidth() << "
feet\n";

getch();
return 0;
}

void Rectangle::Show Width()
{

cout<<"hello: " << pConstRect->GetWidth() <<endl;
}

[Victor Bazarov]

"Dan" <le*********@ya h00.c0m> wrote...

Where do you need it "outside"? In ShowWidth() I want to get pConstRect->GetWidth() , but it do not
work, only in the function where pConstRect has been declared. I need it

to get this information in another function., This is the same problem as the other problem with the radius..
Perhaps you need to give a systematic C++ study a try. You
apparently have no understanding of objects, members, and how
they fit together.

OK, I don't know if this is going to help your efforts or hurt
them in the long run, but here is the solution for you: just
remove the "pConstRect->" from the 'ShowWidth' function.

#include <iostream>
#include <conio.h>
using namespace std;

class Rectangle
{
public:
Rectangle();
~Rectangle();
void SetLength(int length) { itsLength = length; }
int GetLength() const { return itsLength; }

void SetWidth(int width) { itsWidth = width; }
int GetWidth() const { return itsWidth; }

void ShowWidth();

private:
int itsLength;
int itsWidth;
};
Rectangle::Rect angle():
itsWidth(5),
itsLength(10)
{}
Rectangle::~Rec tangle()
{}

int main()
{
Rectangle* pRect = new Rectangle;
const Rectangle * pConstRect = new Rectangle;

cout << "pConstRect width: " << pConstRect->GetWidth() << "
feet\n";

getch();
return 0;
}

void Rectangle::Show Width()
{

cout<<"hello: " << pConstRect->GetWidth() <<endl;
}

[Victor Bazarov]

"Dan" <le*********@ya h00.c0m> wrote...

Just remove its declaration from that function. The member variable
will be used instead of that local one.

There are no declaration in ShowCircle()
and If I remove the one in CreateCircle(), then it still gives me the same
eronous results when I choose to display them ( the other function() )

Dan, you need to sit down either with a good book that would teach
you object-oriented features of C++ step by step, or with a teacher
who will hold your hand while answering all your questions and all
your concerns about that program of yours. I am not a book and the
Usenet is not a good place for hand-holding of pupils. I strongly
recommend you to start over. Without thorough understanding of the
basics you won't be able to move ahead even if we write the program
for you. Start with simpler things. Work your way up. Visit the
alt.comp.lang.l earn.c-c++ newsgroup, it's more for newcomers like
you.

Good luck!

[Dan]

There are no declaration in ShowCircle()
and If I remove the one in CreateCircle(), then it still gives me the same eronous results when I choose to display them ( the other function() )

Dan, you need to sit down either with a good book that would teach
you object-oriented features of C++ step by step, or with a teacher
who will hold your hand while answering all your questions and all
your concerns about that program of yours. I am not a book and the
Usenet is not a good place for hand-holding of pupils. I strongly
recommend you to start over. Without thorough understanding of the
basics you won't be able to move ahead even if we write the program
for you. Start with simpler things. Work your way up. Visit the
alt.comp.lang.l earn.c-c++ newsgroup, it's more for newcomers like
you.

Good luck!

Well I know what you mean, But I am starting over reading my stuff. BUt
like many books I have seen so far, They teach about basic functions and
another chapter about class. But they don't cover all the possibilities
mixing all of those types together and the diferent syntax these involves.
One of the book that I bought, and recently fount it on the net at:
http://newdata.box.sk/bx/c/ seems to be good, But like they tell you what
and how to call a function from the main ( or only one function) tell what
a class is and bl;a bla bla, but but the syntax changes when calling a
function through another function from the same class. Maybe O have not
picked up the right book yet for me or I just can't understand straight.

[John Harrison]

"Dan" <le*********@ya h00.c0m> wrote in message
news:M4******** **********@news 20.bellglobal.c om...

There are no declaration in ShowCircle()
and If I remove the one in CreateCircle(), then it still gives me the same eronous results when I choose to display them ( the other

function() )
Dan, you need to sit down either with a good book that would teach
you object-oriented features of C++ step by step, or with a teacher
who will hold your hand while answering all your questions and all
your concerns about that program of yours. I am not a book and the
Usenet is not a good place for hand-holding of pupils. I strongly
recommend you to start over. Without thorough understanding of the
basics you won't be able to move ahead even if we write the program
for you. Start with simpler things. Work your way up. Visit the
alt.comp.lang.l earn.c-c++ newsgroup, it's more for newcomers like
you.

Good luck!
Well I know what you mean, But I am starting over reading my stuff. BUt
like many books I have seen so far, They teach about basic functions and
another chapter about class. But they don't cover all the possibilities
mixing all of those types together and the diferent syntax these involves.
One of the book that I bought, and recently fount it on the net at:
http://newdata.box.sk/bx/c/ seems to be good, But like they tell you what
and how to call a function from the main ( or only one function) tell

what a class is and bl;a bla bla, but but the syntax changes when calling a
function through another function from the same class. Maybe O have not
picked up the right book yet for me or I just can't understand straight.

Often recommended in this group is Thinking in C++ by Bruce Eckel, free from
www.mindview.net.

Your book looks reasonable (I doubt its legal though) but it is of course
completely impossible to learn C++ in 21 days. Two years is a more likely
figure.

john

[Dan]

>

Well I know what you mean, But I am starting over reading my stuff. BUt
like many books I have seen so far, They teach about basic functions and
another chapter about class. But they don't cover all the possibilities
mixing all of those types together and the diferent syntax these involves.
One of the book that I bought, and recently fount it on the net at:
http://newdata.box.sk/bx/c/ seems to be good, But like they tell you what
and how to call a function from the main ( or only one function) tell what a class is and bl;a bla bla, but but the syntax changes when calling a
function through another function from the same class. Maybe O have not
picked up the right book yet for me or I just can't understand straight.

And again , I am using the same technique as above but with a different
program , this time I not using main but two other functions and it still
wont give me the right answer.This is what I mean , two funtions, two
programs and two different rules this is why I am confused. This below
compiles but showCircle don't give me the right answer.
void Circle::CreateC ircle()
{ Circle * cir = new Circle;

float itsRadius;

cout<<"Enter the radius in cm: " ;
cin>> itsRadius;

cir->SetVolume(itsR adius);
cout<<" Volume: " << cir->GetVolume() <<endl;

}
void Circle::ShowCir cle()
{
cout <<" Volume is : " << GetVolume() <<" cm cube " <<endl;
}

[Victor Bazarov]

"Dan" <le*********@ya h00.c0m> wrote...

Well I know what you mean, But I am starting over reading my stuff. BUt
like many books I have seen so far, They teach about basic functions and another chapter about class. But they don't cover all the possibilities
mixing all of those types together and the diferent syntax these involves. One of the book that I bought, and recently fount it on the net at:
http://newdata.box.sk/bx/c/ seems to be good, But like they tell you what and how to call a function from the main ( or only one function) tell what

a class is and bl;a bla bla, but but the syntax changes when calling a
function through another function from the same class. Maybe O have not
picked up the right book yet for me or I just can't understand

straight.
And again , I am using the same technique as above but with a different
program , this time I not using main but two other functions and it still
wont give me the right answer.This is what I mean , two funtions, two
programs and two different rules this is why I am confused. This below
compiles but showCircle don't give me the right answer.
void Circle::CreateC ircle()
{ Circle * cir = new Circle; ^^^^^^^^^^^^^^^ ^^^^^^^^^^^
Throw this declaration/definition/initialisation out. You don't need it.
float itsRadius;
Throw this declaration/definition out. It screws things up for you.

cout<<"Enter the radius in cm: " ;
cin>> itsRadius;
Now it will read into the _member_ variable. That's what you need.

cir->SetVolume(itsR adius);
Don't use "cir->". Throw "cir->" away. Use "this->":

this->SetVolume(itsR adius);
cout<<" Volume: " << cir->GetVolume() <<endl;
Again, replace "cir->" with "this->".

}
void Circle::ShowCir cle()
{
cout <<" Volume is : " << GetVolume() <<" cm cube " <<endl;
}

Learning C++ like this is detrimental to the cause. You should use
_systematic_ _study_. Do you understand the word "systematic "?

[Thomas Matthews]

Dan wrote:

Hello,

I have trouble with class calling. I am calling getvolume() with succes in
the function CreateCircle but it do not want to call it in ShowCircle()
function. I am staying in the same class. I thought that was the point of
encapsulation. When the function ShowCircle() is called I get very large
number -1.07374e+008
can anyone help me ?
class Circle
{
public:

Circle (int radius){
itsRadius = 0; }
void CreateCircle();
void ShowCircle();

void SetVolume( float radius){
volume = PI * pow(radius,2); }
float GetVolume(){ return volume; }

private:
float itsRadius;
float volume;
};

BTW, circles don't have volumes, they have areas.
Cylinders, spheres and cones have volumes.
Three dimensional objects have volumes, two
dimensional have areas.

The same with rectangles and boxes. Rectangles
have areas, boxes have volume.

--
Thomas Matthews

C++ newsgroup welcome message:
http://www.slack.net/~shiva/welcome.txt
C++ Faq: http://www.parashift.com/c++-faq-lite
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alt.comp.lang.l earn.c-c++ faq:
http://www.raos.demon.uk/acllc-c++/faq.html
Other sites:
http://www.josuttis.com -- C++ STL Library book
http://www.sgi.com/tech/stl -- Standard Template Library

[Dan]

> > void Circle::CreateC ircle()

{ Circle * cir = new Circle;

^^^^^^^^^^^^^^^ ^^^^^^^^^^^
Throw this declaration/definition/initialisation out. You don't need it.

float itsRadius;

Throw this declaration/definition out. It screws things up for you.

cout<<"Enter the radius in cm: " ;
cin>> itsRadius;

Now it will read into the _member_ variable. That's what you need.

cir->SetVolume(itsR adius);

Don't use "cir->". Throw "cir->" away. Use "this->":

this->SetVolume(itsR adius);

cout<<" Volume: " << cir->GetVolume() <<endl;

Again, replace "cir->" with "this->".

}
void Circle::ShowCir cle()
{
cout <<" Volume is : " << GetVolume() <<" cm cube " <<endl;
}

Learning C++ like this is detrimental to the cause. You should use
_systematic_ _study_. Do you understand the word "systematic "?

Thanks for the help, Ya I know what systematic means. BUt I think learning
a new language is confusing, or this could only be me. I did the
modification but , I still don't get a value for Getvolume in ShowCircle.
Would passing those values by reference work ? right now I have only one
value , but later I would like to create many circles and store them into an
array. Would your method work ? I tried using pointer and passing by
reference but with no luck, but if you tell me thats the way I will do
more work on it.
thanks

[Dan]

BTW, circles don't have volumes, they have areas.
Cylinders, spheres and cones have volumes.
Three dimensional objects have volumes, two
dimensional have areas.

The same with rectangles and boxes. Rectangles
have areas, boxes have volume.

I know that , I just want to get the program, or part of it working, I dont
need to be mathematically correct for now.