WHy should virtual methods be explicitly overridden in C#?

Question

Why should virtual methods be explicitly overridden in C#?

Answer 1

If you don't add the override keyword, the method will be hidden (as if it had the new keyword), not overridden.

For example:

class Base {
    public virtual void T() { Console.WriteLine("Base"); }
}
class Derived : Base {
    public void T() { Console.WriteLine("Derived"); }
}

Base d = new Derived();
d.T();

This code prints Base. If you add override to the Derived implementation, the code will print Derived.

You cannot do this in C++ with a virtual method. (There is no way to hide a C++ virtual method without overriding it)