Virtual Keyword in CPP

//Use of Virtual Keyword in CPP
#include<iostream.h>
#include<conio.h>
class A
{
 protected:
 int a;
};
class B:public virtual A
{
 protected:
 int b;
};
class C:public virtual A
{
 protected:
 int c;
};
class D:public virtual A
{
 protected:
 int d;
};
class E:public virtual B,public virtual C
{
 protected:
 int e;
};
class F:public virtual C,public virtual D
{
 protected:
 int f;
};
class G:public E,F
{
 private:
 int g;
 public:
 void getdata()
 {
  cout<<"Enter 7 values\n";
  cin>>a>>b>>c>>d>>e>>f>>g;
 }
 void showdata()
 {
  cout<<"\nFirst value="<<a;
  cout<<"\nSecond value="<<b;
  cout<<"\nThird value="<<c;
  cout<<"\nFourth value="<<d;
  cout<<"\nFifth value="<<e;
  cout<<"\nSixth value="<<f;
  cout<<"\nseventh value="<<g;
 }
};
void main()
{
 clrscr();
 G x;
 x.getdata();
 x.showdata();
 getch();
}