C# multiple inheritance, using protected member

Question

I have little problem using inheritance. I can neither change the value of first and second in class C nor first in class B when they are protected. If these variables are public everything works fine, but in this case what's the point of using protected?

class A
{
    protected int first { get; set; }
}

class B : A
{
    protected int second { get; set; }

    public Show() 
    {
        A a = new A();
        a.first = 5;
    }
}

class C : B
{
    private int third { get; set; }

    static void Main()
    {
        B b = new B();
        b.first = 1;
        b.second = 2;
    }
}

Answer 1

The main problem is simply caused by you putting your program's entry point inside the class you want to test. Because Main() is static, you can't access C's (inherited) instance members.

So separate it:

class Program
{
    static void Main()
    {
        C c = new C();
        c.Test();
    }
}

Your class C inherits from B, so C can access B's protected members like so:

class C : B
{
    private int third { get; set; }

    public void Test()
    {
        first = 1; // from A
        second = 2; // from B
        third = 3; // from C
    }
}

By newing a B inside C, there's no relation between those instances of B and C, so all you can access there are B's public and internal members.