Answer 1

Pure virtual function is initialized with zero. Im this way, we create abstract classes in C++. Moreover, this technique can be used for creating interfaces as in Java. No object can be instantiated from the class that contains pure virtual functions. These functions have to be overriden by the class that inherits that abstract class.

Example
class io {
public:
void read () = 0;
void show () = 0;
};

class demo : public io {
private:
int x;
public:
void read () {cin>>x;}
void show () {cout<<x;}
}