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;
}

[John Harrison]

"Dan" <le*********@ya h00.c0m> wrote in message
news:fr******** ******@news20.b ellglobal.com.. .

void Circle::Display () const
{
cout<<"CenterPo int: " << GetCenterPoint( ) << endl <<"Radius: " <<
GetRadius() <<endl <<"Area: " << GetArea() <<endl;
}

You showed me this function. I would say that is good for one value, cause
Get Radius will get one value from that function in the class. But I need to save those values into an array. Up to ten times because my array is only that long.

Right. There is nothing in the above function to stop you calling it ten
times for ten different objects

Circle circle[10];

for (int i = 0; i < 10; i++)
{
cout << "circle #" << i + 1 << " " << circle[i].Display() << endl;
}

This is how you write class methods, the class method works for *one* object
(usually), you then call it as many times as you need for as many different
objects as you have. This is more flexible and simpler.

john

[John Harrison]

"Dan" <le*********@ya h00.c0m> wrote in message
news:_b******** *****@news20.be llglobal.com...

class Circle : public Shape
{
public:
Circle(Point center, float radius) : Shape(center), _radius(radius)
{
}
I don't get this _radius(radius

Its more or less the same as this

Circle(Point center, float radius) : Shape(center)
{
_radius = radius;
}

But there are situations when the first form is better, look up initialiser
lists in your favourite C++ book. But its a minor point, no big deal.

float Circle::GetArea () const
{
return PI * pow(radius,2);
Ya thats smart, one function instead of one , neat.

The Display method doesn't take all those incorrect parameters, the

Display

method displays a circle using the class member variables and methods, its does not pick a Circle from an array and display that.

You could write a function to pick a circle from and array if you wanted

to,

but that function should not be a member of the Circle class.

Did you tell me the other day that whenever I leave a function I also

loose my information unless it is in an array ?? so This is why I was doing that
You lose information from variables (and arrays) which are local to that
function (unless you return them from that function). But class member
variables are not local to any one function, they are only destroyed when
the object itself is destroyed.

I think this is the most important thing you aren't getting. The lifetime
and scope of objects and variables. I guess the only answer is more practice
and study. I'd still advise you work with a simpler program. For instance
its not a good idea to be trying to learn inheritance as well, while you are
still struggling with the basics of objects and classes.

Really you should start again, I know it difficult to do this, but you are really flogging a dead horse with your current code. Make the Circle class look like the one I have above, same for the other classes. Then declare
your arrays like this

Circle circle[10];
Cylinder cylinder[10];
Triangle triangle[10];
int count_circle;
int count_cylinder;
int count_triangle;
Ok creating an array there is fine ( along my menu)
But I need to pass the array to my function no ?

Maybe see below
The user is going have to
put in his information, and that information will be put in Circle array. If I just call a void function in my menu how can I insert that information
into my array. ? This is my problem in c++ is how to point object put
and take values and being to play as much as.. well as need anyway

I think you were doing that more or less OK, there were two problems, first
you had two different arrays, secondly your CreateCircle function was
wrongly part of the Circle class.

Something like this should do the trick, this is using a return value.

void menu()
{
Circle circle[10];
Cylinder cylinder[10];
Triangle triangle[10];
int count_circle = 0;
int count_cylinder = 0;
int count_triangle = 0;

switch (...)
{
case ...:
circle[count_circle] = CreateCircle();
count_circle++;
break;
...
}
}

Circle CreateCircle()
{
cout << "enter circle radius ";
float radius;
cin >> radius;
cout << "enter circle center point";
Point center;
cin >> center;
return Circle(center, radius);
}

but you could do it with parameters like you were doing, the important thing
is that CreateCircle is not, and doesn't need to be, part of the Circle
class.
I tried adding the const atthe end of the function but I get this error:
DisplayCircle' : overloaded member function 'void (void)' not found in
'Circle'

Probably you didn't add it in both places.

class Circle
{
void DisplayCircle() const; // const here
};

void Circle::Display () const // and here
{
...
}

but it not a big deal for you at the moment (its an important topic for
later) so leave it out if it is causing problems.
And if you are not passing anything with you void function, how can you keep track of you count if it was created in the menu function.?
BTW , where do you live ?
and thanks a million for you help John

[John Harrison]

> Right. There is nothing in the above function to stop you calling it ten

times for ten different objects

Circle circle[10];

for (int i = 0; i < 10; i++)
{
cout << "circle #" << i + 1 << " " << circle[i].Display() << endl;
}

This is how you write class methods, the class method works for *one* object (usually), you then call it as many times as you need for as many different objects as you have. This is more flexible and simpler.

Sorry the above code is garbage, something like this is what I meant

Circle circle[10];

for (int i = 0; i < 10; i++)
{
cout << "circle #" << i + 1 << endl;
circle[i].Display();
}

john

[Dan]

> Circle circle[10];

for (int i = 0; i < 10; i++)
{
cout << "circle #" << i + 1 << " " << circle[i].Display() << endl;
}

This is how you write class methods, the class method works for *one* object (usually), you then call it as many times as you need for as many different objects as you have. This is more flexible and simpler.

Ok I tried this , but it still not showing me the right radius value,
I am passing it by reference, and my count by value.
class Circle: public Shape
{
public:
Circle(){};
Circle(Point p, float r) : Shape(p) {radius = r;
cout<<"rad:" << radius; }

void CreateCircle() ;
void DisplayCircle(C ircle* circle ,int);

float GetArea(){ return PI * ( pow(radius,2) ); }

private:
float radius;

};

void Circle::Display Circle(Circle* circle, int count_circle)
{
if ( (count_circle) <= 0)
{ cout<< "There are no Circles to display! Please choose another option "
<<endl; }
else
{
for (int i=0; i< (count_circle); i++)
{
cout<<" Here is the area for circle #" << i+1 <<endl;
cout <<"Area: " << circle[i].GetArea() <<endl;
cout <<endl;
}
}
}

and in my switch :
( and this is where I initialize the Circle array and counter.

case '1':
circle[count_circle].CreateCircle() ;
count_circle++;
break;

[Dan]

void menu()
{
Circle circle[10];
Cylinder cylinder[10];
Triangle triangle[10];
int count_circle = 0;
int count_cylinder = 0;
int count_triangle = 0;

switch (...)
{
case ...:
circle[count_circle] = CreateCircle();
count_circle++;
break;

This is giving me an error,: undeclared identifier
so I used this:
circle[count_circle]=circle.CreateC ircle();
but then error: '.CreateCircle' must have class/struct/union type

But It is, circle is the object , and that object is calling the function.
This is what I am seeing in my documentation.
The problem is , that books gives you a very basic example of classes,
functions, but very rarely a mixed of all that. This is why I am having
problem manipulating the information, but not so much with the basic coding
and syntax.

[John Harrison]

"Dan" <le*********@ya h00.c0m> wrote in message
news:HF******** ******@news20.b ellglobal.com.. .

Circle circle[10];

for (int i = 0; i < 10; i++)
{
cout << "circle #" << i + 1 << " " << circle[i].Display() << endl;
}

This is how you write class methods, the class method works for *one* object

(usually), you then call it as many times as you need for as many

different

objects as you have. This is more flexible and simpler.

Ok I tried this , but it still not showing me the right radius value,
I am passing it by reference, and my count by value.
class Circle: public Shape
{
public:
Circle(){};
Circle(Point p, float r) : Shape(p) {radius = r;
cout<<"rad:" << radius; }

void CreateCircle() ;
void DisplayCircle(C ircle* circle ,int);

float GetArea(){ return PI * ( pow(radius,2) ); }

private:
float radius;

};

void Circle::Display Circle(Circle* circle, int count_circle)
{
if ( (count_circle) <= 0)
{ cout<< "There are no Circles to display! Please choose another option

" <<endl; }
else
{
for (int i=0; i< (count_circle); i++)
{
cout<<" Here is the area for circle #" << i+1 <<endl;
cout <<"Area: " << circle[i].GetArea() <<endl;
cout <<endl;
}
}
}

and in my switch :
( and this is where I initialize the Circle array and counter.

case '1':
circle[count_circle].CreateCircle() ;
count_circle++;
break;

You're making the same mistake again!!! You've got everything I said
backwards, Sorry but I give up.

john

[John Harrison]

"Dan" <le*********@ya h00.c0m> wrote in message
news:0g******** ******@news20.b ellglobal.com.. .

void menu()
{
Circle circle[10];
Cylinder cylinder[10];
Triangle triangle[10];
int count_circle = 0;
int count_cylinder = 0;
int count_triangle = 0;

switch (...)
{
case ...:
circle[count_circle] = CreateCircle();
count_circle++;
break;
This is giving me an error,: undeclared identifier
so I used this:
circle[count_circle]=circle.CreateC ircle();
but then error: '.CreateCircle' must have class/struct/union type

Jesus, look at the code I wrote

circle[count_circle] = CreateCircle();

look at the code you wrote

circle[count_circle]=circle.CreateC ircle();

See the difference? In my version CreateCircle is *not* a member of the
Circle class, I really don't know why you think it should be. I said it
should not in black and white.
The problem is , that books gives you a very basic example of classes,
functions, but very rarely a mixed of all that. This is why I am having
problem manipulating the information, but not so much with the basic coding and syntax.

Yes I can see that. Work with simpler examples until you get it

john

[John Harrison]

>

You're making the same mistake again!!! You've got everything I said
backwards, Sorry but I give up.

Sorry about that but I think newsgroups are not a good place to learn the
kind of things you need to learn. As you realise you're struggling with
concepts not with syntax (your syntax is pretty good). What you really need
is a teacher who can explain this kind of stuff to you. I don't think you
are going to get it from a newsgroup, it just not the right medium.

John

[Dan]

>

Jesus, look at the code I wrote

circle[count_circle] = CreateCircle();

look at the code you wrote

circle[count_circle]=circle.CreateC ircle();

I thought that was not good encapsulation. I was just trying to put whatever
is concern with circle in the Circle class. Now you are asking me to make
CreateCircle global right ?

[Dan]

"John Harrison" <jo************ *@hotmail.com> wrote in message
news:2j******** ****@uni-berlin.de...

You're making the same mistake again!!! You've got everything I said
backwards, Sorry but I give up.

Sorry about that but I think newsgroups are not a good place to learn the
kind of things you need to learn. As you realise you're struggling with
concepts not with syntax (your syntax is pretty good). What you really

need is a teacher who can explain this kind of stuff to you. I don't think you
are going to get it from a newsgroup, it just not the right medium.

John

I know I am trying to learn this, and I know I am not the fastest person on
earth to learn this crap. BUt this is where I am at know. I know how
function arryas and classes work individually, but when comes time to mixe
them all up together I'm mixed up, I have been working on this since 8:00
this morning and I have not advanced very much. Thanks for you help and all
those posts. I will be reading all those posts again now see if I missed
anything.
D