Наследование. Не могу понять элементарную вещь

class Based {
     int val;
public:
     Based(int v) : val(v) { }
};
 
class Derived : public Based {
     int val;
public:
      Derived(int v) : val(v), Based(v) { }
};
 
int main() {
       Based *ptr;
       Derived obj(5);
       ptr = &obj;
        return 0;
}

class Based
{
    void method() {}
    
public:
    Based() {}
};
 
class Derived : public Based
{
public:
    Derived() 
        : Based()
    {
        method(); // ошибка: 'void Based::method()' is private within this context
    }
};

class Based
{
    Based() {}
};
 
class Derived : public Based
{
public:
    Derived() 
        : Based() // ошибка: 'Based::Based()' is private within this context
    { 
    }
};

class Based
{
public:
     Based() {}
 
     void method()
     {
         std::cout << "Based" << std::endl;
     }
};
 
class Derived : public Based
{
public:
      Derived() : Based() {}
 
      void method()
      {
          std::cout << "Derived" << std::endl;
      }
};
 
int main(int argc, char *argv[])
{
    Based *ptr;
    Derived obj;
    obj.method();  // выведет Derived
 
    ptr = static_cast<Based*>(&obj);
    ptr->method(); // выведет Based
 
    return 0;
}

class Based {
     int val;
public:
     Based(int v) : val(v) { }
};
 
class Derived : Based {
     int val;
public:
      Derived(int v) : val(v), Based(v) { }
};
 
int main() {
       Based *ptr;
       Derived obj(5);
  //     ptr = &obj;
        return 0;
}

     Derived obj(5);

      ptr = &obj;

 Derived obj(5)