Abstract Class in C#

Abstract Class

1. "Abstract classes are useful when you need a class for the purpose of inheritance and polymorphism"
2. The purpose of an abstract class is to provide default functionality to its subclasses
3. When a class contains at least one abstract method, then the class must be declared as an abstract class
4. It is mandatory to override the abstract method in the derived class
5. When a class is declared as an abstract class, then it is not possible to create an instance for that class
6. But it can be used as a parameter in a method

using System;

public abstract class Calculation

{

public abstract int sum(int a, int b); // an abstract class has no body ie no implementaiton

public int multiply(int a, int b) // this is non-abstract method

{

return (a * b);

}

}

public class Test : Calculation

{

public static void Main()