Compare Virtual methods and Abstract methods in c#

Any Virtual method must have a default implementation, and it can be overridden in the derived class using the override keyword. On the contrary, an Abstract method doesn’t have an implementation, and it resides in the abstract class. The derived class must implement the abstract method. Though not necessary, we can use an override keyword here.

public abstract class E
{
    public abstract void AbstractMethod(int i);
    public virtual void VirtualMethod(int i)
    {
        // Default implementation which can be overridden by subclasses.
    }
}
public class D : E
{
    public override void AbstractMethod(int i)
    {
        // You HAVE to override this method
    }
    public override void VirtualMethod(int i)
    {
        // You are allowed to override this method.
    }
}