### virtual function = 0

Hi everybody

i have a question. Why is in this code

 ``1234567`` ``````class Body { public: virtual double Volume() = 0 { } virtual double Surface() = 0 { } }``````

equating to zero?

Thanks
It is called pure virtual or abstract function and requires to be overwritten in an derived class.
The syntax above is wrong, To have pure virtual functions you should have this:
 ``12345`` ``````class Body { public: virtual double Volume() = 0; virtual double Surface() = 0; };``````
( No function bodies )
But it translates VS2011 without errors...
So, everywhere, when i can use virtual/abstract function i must get the equating to zero, why is that? What be done, when i won't use this equating? I mean just use

`virtual type Function();`

without function bodies and the equating to zero
A pure virtual function makes its class abstract, because it cannot be instantiated.
To finchCZ
You need to learn up on Classes and polymorphism
yes i know, so i asked a question, because i want to learn it

thanks for help anyway
FYI everyone, you CAN give a pure virtual function a definition, it just won't be used.

http://www.parashift.com/c++-faq-lite/abcs.html#faq-22.4
Not sure if I understood that, so you can make a function purely virtual which prevents the instantiation of the base class, but you can still call it from a derived class or what? Otherwise I wouldn't see any point in providing a definition for an abstract function.
You can still call it though.
If you give a definition, you cannot instantiate the class, as per a normal pure virtual function. Basically all it does is let you possibly define some common functionality that derived classes might want.
This is what I mean (although I have not sen it in practice)
 ``123456789101112131415161718192021222324252627282930313233343536373839404142`` ``````class Base { public: virtual void VFuncA()=0; int x; }; //Give the pure virtual function a body void Base::VFuncA() { x =3; } class Derived: public Base { public: void VFuncA() { Base::VFuncA();//calls bas class version } }; int _tmain(int argc, _TCHAR* argv[]) { //Base *pb = new Base;//Error base class is abstract Base *pb = new Derived; pb->VFuncA(); delete pb; return 0; }``````
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