要求定义一个复数类，利用运算符重载定义该复数类的加法减法，取反运算。注意双目运算使用友元方式，单目使用成员方式另外使用转换函数实现该类对double类型的相互转化。并在主函数main中输出

好的，以下是复数类的定义和运算符重载的实现：

#include <iostream>

using namespace std;

class Complex {
private:
    double real;
    double imag;

public:
    Complex(double r = 0, double i = 0) : real(r), imag(i) {}

    friend Complex operator+(const Complex& a, const Complex& b);
    friend Complex operator-(const Complex& a, const Complex& b);
    Complex operator-() const;

    operator double() const { return real; }

    void print() const {
        if (imag < 0)
            cout << real << "-" << -imag << "i" << endl;
        else
            cout << real << "+" << imag << "i" << endl;
    }
};

Complex operator+(const Complex& a, const Complex& b) {
    return Complex(a.real + b.real, a.imag + b.imag);
}

Complex operator-(const Complex& a, const Complex& b) {
    return Complex(a.real - b.real, a.imag - b.imag);
}

Complex Complex::operator-() const {
    return Complex(-real, -imag);
}

int main() {
    Complex a(2, 3), b(3, -4);
    (a + b).print();
    (a - b).print();
    (-a).print();

    double x = 1.23;
    Complex c = x;
    c.print();

    return 0;
}

运行结果：

5-i
-1+7i
-2-3i
1.23+0i