C-plus编码错误

我正在学习C++,我必须完成一个面向对象的程序。我很难理解为什么我会出错。请在解释时尽可能详细地说明,因为这将有助于我自学C++的过程。以下是我的初始代码和错误:

#include<iostream>
using namespace std;

class RectangularCube { //Defined the class Rectangular Cube
    private: //Access specifier - Declare two sides as private data field
        string color; //Private data field color that is string type
        double width;
        double height;

    public:
    double length; //Declare one side as a public data field

    //Contructor with parameteres
    RectangularCube(string newColor, double newWidth, double newHeight, double newLength) {
        color = newColor;
        width = newWidth;
        height = newHeight;
        length = newLength;
    }

    RectangularCube() { //No-arguments contructor with all three sides and color set to different values
        color = black;
        width = 5.145;
        height = 4.894;
        length = 10.123;
    }

    // Return Volume of this Rectangular Cube
    double getVolume() {
        return length * width * height;
    };

    //Return Surface Area of this Rectangular Cube
    double getSurfaceArea() {
        return 2(length * width) + 2(length * height) + 2(width * height)
    };
    
    //get and set functions for the two private sides and color data field
    double getColor();
    double getWidth();
    double getHeight();
    void setColor();
    void setWidth();
    void setHeight();

};

int main() {
    RectangularCube rectangularcube1();

    cout << "The Volume of the Rectangular Cube is: "
        << rectangularcube1.getVolume() << endl;
    return 0;
}

错误

            color = black;
                    ^
RectangularCube.cpp:35:21: error: called object type 'int' is not a function or function pointer
            return 2(length * width) + 2(length * height) + 2(width * height)
                   ~^
RectangularCube.cpp:35:41: error: called object type 'int' is not a function or function pointer
            return 2(length * width) + 2(length * height) + 2(width * height)
                                       ~^
RectangularCube.cpp:35:62: error: called object type 'int' is not a function or function pointer
            return 2(length * width) + 2(length * height) + 2(width * height)
                                                            ~^
4 errors generated.