What is the use of virtual keyword in C#?

Question

When to use virtual keyword?
What is the purpose of virtual keyword in C#?

Answer 1

virtual is a keyword related to polymorphism. It's usually paired with the override keyword.

public class A
{
public virtual int f() {return 1;}
}
public class B : A
{
public override int f() {return 2;}
}

Polymorphism basically means having many form, and virtual is one of the ways to do it.

Saying you have this:

A obj;

At some point you do this:

obj.f();

There will be 2 possible output.

1 if obj is initialized with A(),
2 if obj is initialized with B(),

There is third but it's an error which obj is not initialized.