访问说明符,无法调用派生 class 中定义的函数

Access specifier, not able to call a function which is defined in the derived class

我试图了解 C++ 中的访问说明符,所以我从基 class 访问 public 和受保护成员,并在派生 class 中执行添加函数如下所示,

#include<iostream>
using namespace std;

class Base
{
    public:
        int a;
    protected:
        int b;
};

class Derived : public Base
{
    public:
        int sum;
        void add()
        {   
            a = 10;
            b = 20;
            sum = a + b;
        }
};


int main()
{
    Derived Obj;
    Obj.add;
    cout << "The sum : " << Obj.sum << "\n";
    return 0;
}   

但是在编译时我收到以下错误消息"statement cannot resolve address of the overload function"谁能解释一下错误是什么?

提前致谢

函数调用在以下行中缺少括号:

Obj.add;

应该是:Obj.add();