使用C++编写一个复数类的例子，重载 +、 - 、= 运算符，进而实现复数加、减、赋值运算；

以下是一个简单的复数类的实现，包括重载 +、-、= 运算符，可以实现复数的加、减、赋值运算：

#include <iostream>

using namespace std;

class Complex {
public:
    Complex(double r = 0, double i = 0) : real(r), imag(i) {}
    Complex operator+(const Complex& c) const;
    Complex operator-(const Complex& c) const;
    Complex& operator=(const Complex& c);

    friend ostream& operator<<(ostream& os, const Complex& c);

private:
    double real;
    double imag;
};

Complex Complex::operator+(const Complex& c) const
{
    return Complex(this->real + c.real, this->imag + c.imag);
}

Complex Complex::operator-(const Complex& c) const
{
    return Complex(this->real - c.real, this->imag - c.imag);
}

Complex& Complex::operator=(const Complex& c)
{
    this->real = c.real;
    this->imag = c.imag;
    return *this;
}

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

int main()
{
    Complex c1(1, 2);
    Complex c2(3, 4);

    cout << "c1 = " << c1 << endl;
    cout << "c2 = " << c2 << endl;

    Complex c3 = c1 + c2;
    cout << "c3 = " << c3 << endl;

    Complex c4 = c1 - c2;
    cout << "c4 = " << c4 << endl;

    c1 = c2;
    cout << "c1 = " << c1 << endl;

    return 0;
}

输出结果为：

c1 = 1 + 2i
c2 = 3 + 4i
c3 = 4 + 6i
c4 = -2 - 2i
c1 = 3 + 4i

可以看到，我们成功地实现了复数类，并且可以进行复数的加、减、赋值运算。