编写一个计算器的C++类，能够完成两个数的求和、相乘、相除，开根号、平方功能。

可以创建一个名为`Calculator`的C++类，这个类会包含私有成员变量以及公有成员函数来实现所需的操作。以下是简单的类设计：

#include <iostream>
#include <cmath> // 包含数学库，用于计算根号和平方

class Calculator {
private:
    double num1;
    double num2;

public:
    // 构造函数，初始化两个数字
    Calculator(double a = 0, double b = 0) : num1(a), num2(b) {}

    // 求和
    double add() const { return num1 + num2; }
    
    // 相乘
    double multiply() const { return num1 * num2; }

    // 相除 (处理除数为零的情况)
    double divide(double divisor) const {
        if (divisor != 0) {
            return num1 / divisor;
        } else {
            throw std::runtime_error("Division by zero is not allowed.");
        }
    }

    // 开根号
    double square_root() const {
        if (num1 >= 0) {
            return sqrt(num1);
        } else {
            throw std::runtime_error("Square root of negative number is undefined.");
        }
    }

    // 平方
    double square() const { return num1 * num1; }

    // 显示结果的友元函数，方便外部获取计算结果
    friend std::ostream& operator<<(std::ostream& os, const Calculator& calc);
};

// 输出运算结果到流
std::ostream& operator<<(std::ostream& os, const Calculator& calc) {
    os << "Result for operation: ";
    os << "Sum: " << calc.add() << "\n";
    os << "Product: " << calc.multiply() << "\n";
    try {
        os << "Quotient: " << calc.divide(2) << "\n"; // 示例除以2
    } catch (const std::exception& e) {
        os << e.what() << "\n";
    }
    os << "Square Root: " << calc.square_root() << "\n";
    os << "Square: " << calc.square() << "\n";
    return os;
}

int main() {
    Calculator calculator(5, 3);
    std::cout << calculator << std::endl;
    return 0;
}