定义一个复数类complex，利用重载实现复数的四则运算

以下是一个定义复数类Complex并利用运算符重载实现复数的四则运算的示例：

#include <iostream>
using namespace std;

class Complex {
private:
    double real;
    double imag;

public:
    Complex() {
        real = 0.0;
        imag = 0.0;
    }

    Complex(double r) {
        real = r;
        imag = 0.0;
    }

    Complex(double r, double i) {
        real = r;
        imag = i;
    }

    Complex operator+(const Complex& c) {
        Complex result;
        result.real = real + c.real;
        result.imag = imag + c.imag;
        return result;
    }

    Complex operator-(const Complex& c) {
        Complex result;
        result.real = real - c.real;
        result.imag = imag - c.imag;
        return result;
    }

    Complex operator*(const Complex& c) {
        Complex result;
        result.real = real * c.real - imag * c.imag;
        result.imag = real * c.imag + imag * c.real;
        return result;
    }

    Complex operator/(const Complex& c) {
        Complex result;
        double denominator = c.real * c.real + c.imag * c.imag;
        result.real = (real * c.real + imag * c.imag) / denominator;
        result.imag = (imag * c.real - real * c.imag) / denominator;
        return result;
    }

    friend ostream& operator<<(ostream& os, const Complex& c) {
        os << c.real << " + " << c.imag << "i";
        return os;
    }
};

int main() {
    Complex c1(2.0, 3.0);
    Complex c2(1.0, 2.0);

    Complex sum = c1 + c2;
    Complex difference = c1 - c2;
    Complex product = c1 * c2;
    Complex quotient = c1 / c2;

    cout << "Sum: " << sum << endl;
    cout << "Difference: " << difference << endl;
    cout << "Product: " << product << endl;
    cout << "Quotient: " << quotient << endl;

    return 0;
}