#include<iostream.h>
#include<conio.h>
class A
{
         public:
         void showA()
         {
                  cout<<"This is Class A";
          }
};
class B:virtual public A
{
       public:
       void showB()
       {
                  cout<<"This is class B";
        }
};
class C:virtual public A
{
       public:
       void showC()
       {
             cout<<"This is class C";
       }
};
class D:public B,pubic C
{
       public:
       void showD()
      {
            cout<<"This is class D";
      }
};
void main()
{
       D D1;
       D1.showA();
       D1.showB();
       D1.showC();
       D1.showD();
       getch();
}

OUTPUT;

This is class A
This is class B
This is class C
This is class D

#include<iostream.h>
#include<conio.h>

void main()
{
    float a,b,ans;
    int choice;
    clrscr();
    cout<<"\n1.Addition\n2.Subtraction";
    cout<<"\n3.Multiplication\n4.Division";
    cout<<"\nEnter your choice(1 to 4) : ";
    cin>>choice;
    cout<<"Enter value of A & B : ";
    cin>>a>>b;

    switch(choice)
    {
        case 1:ans=a+b;
               break;
        case 2:ans=a-b;
               break;
        case 3:ans=a*b;
               break;
        case 4:ans=a/b;
               break;
        default:cout<<"Wrong Choice....";
    };
    cout<<"Answer = "<<ans;
    getch();
}

OutPut:

1.Addition
2.Subtraction
3.Multiplication
4.Division
Enter your choice(1 to 4) : 1

Enter value of A & B : 5  6
Answer = 11