What is an Abstract Class in C#?

An Abstract class is a class which is denoted by abstract keyword and can be used only as a Base class. An Abstract class should always be inherited. An instance of the class itself cannot be created. If we do not want any program to create an object of a class, then such classes can be made abstract.

Any method in the abstract class does not have implementations in the same class. But they must be implemented in the child class.

abstract class AB1
{
Public void Add();
}
Class childClass : AB1
{
childClass cs = new childClass ();
int Sum = cs.Add();
}

All the methods in an abstract class are implicitly virtual methods. Hence virtual keyword should not be used with any methods in  abstract class.