1）类的封装性 3-34，声明复数类Complex，成员变量包括实部和虚部，成员方法包括实现由字符串构造复数、复数加法、减法、字符串描述、比较相等、计算复数的模√实部+虚部等操作。复数语法图如图3-16所示。

答：可以使用以下代码实现：

class Complex {
private:
    double real;
    double imag;
public:
    Complex(double r = 0, double i = 0) : real(r), imag(i) {}
    Complex(const std::string& str) {
        std::stringstream ss(str);
        char ch;
        ss >> real >> ch >> imag;
    }
    Complex operator+(const Complex& other) const {
        return Complex(real + other.real, imag + other.imag);
    }
    Complex operator-(const Complex& other) const {
        return Complex(real - other.real, imag - other.imag);
    }
    bool operator==(const Complex& other) const {
        return real == other.real && imag == other.imag;
    }
    double mod() const {
        return std::sqrt(real * real + imag * imag);
    }
    std::string to_string() const {
        std::stringstream ss;
        ss << real << "+" << imag << "i";
        return ss.str();
    }
};

这个类实现了复数的加法、减法、比较相等、计算模以及字符串描述等操作。可以使用以下代码测试：

Complex c1(1, 2);
Complex c2("3+4i");
Complex c3 = c1 + c2;
Complex c4 = c1 - c2;
std::cout << c1.to_string() << std::endl;
std::cout << c2.to_string() << std::endl;
std::cout << c3.to_string() << std::endl;
std::cout << c4.to_string() << std::endl;
std::cout << (c1 == c2) << std::endl;
std::cout << c1.mod() << std::endl;