Question

Lets say that we have the following code

Base() { ... }

Derived : Base { ... }

Main() 
{
    var derivedInstance = new Derived();

    if(derivedInstance is Base)
    {
         DoStuff();
    }
}

The if statement that we have returns true. How do I differentiate between the derived type from the base type when I am working with a derived instance.

Essentially, I want the above if statement to return false, but not sure how to accomplish this.

Answer 1

Try

if (derivedInstance.GetType() == typeof(Base)) {
    DoStuff();
}

However, this looks rather strange. What are you trying to do?
What about having a virtual method defined in your base class:

class Base { 
    public virtual void DoStuff() {
        // actually do something
    }
}
class Derived { 
    public virtual override void DoStuff() {
        // do nothing
    }
}

And then you could just call DoStuff() on the instance, without checking its type.