任务3 源代码：

Complex.hpp

#pragma onnce
#include <iostream>
#include <cmath>

class Complex
{
    friend Complex add(const Complex &, const Complex &);
    friend bool is_equal(const Complex &, const Complex &);
    friend double abs(const Complex &);
    
public:
    Complex(const double &r = 0, const double &i = 0) : real{r}, imag{i} { ; }
    Complex(const Complex &c) : real{c.real}, imag{c.imag} { ; }
    ~Complex() = default;
    double get_real() const;
    double get_imag() const;
    void show() const;
    void add(const Complex &c);

private:
    double real;
    double imag;
};

double Complex::get_real() const { return this->real; }
double Complex::get_imag() const { return this->imag; }
void Complex::show() const
{
    using std::cout;
    cout << this->real;
    if(this->imag == 0)
        return;
    else
    {
        if(this->imag < 0)
            cout << " - ";
        else 
            cout << " + ";
        cout << fabs(this->imag) << "i";
    }
}
void Complex::add(const Complex &c)
{
    this->real += c.real;
    this->imag += c.imag;
}


inline Complex add(const Complex &c1, const Complex &c2)
{
    Complex c3(c1.real + c2.real, c1.imag + c2.imag);
    return c3;
}
inline bool is_equal(const Complex &c1, const Complex &c2)
{
    return c1.real == c2.real && c1.imag == c2.imag;
}
inline double abs(const Complex &c)
{
    return sqrt(c.real * c.real + c.imag * c.imag);
}

task3.cpp

#include "Complex.hpp"
#include <iostream>

int main()
{
    using namespace std;

    Complex c1(3.6666, -10.0001);
    const Complex c2(13.5555);
    Complex c3(c1);

    cout << "c1 = ";
    c1.show();
    cout << endl;

    cout << "c2 = ";
    c2.show();
    cout << endl;
    cout << "c2.imag = " << c2.get_imag() << endl;

    cout << "c3 = ";
    c3.show();
    cout << endl;

    cout << "abs(c1) = ";
    cout << abs(c1) << endl;

    cout << boolalpha;
    cout << "c1 == c3 : " << is_equal(c1, c3) << endl;
    cout << "c1 == c2 : " << is_equal(c1, c2) << endl;

    Complex c4;
    c4 = add(c1, c2);
    cout << "c4 = c1 + c2 = ";
    c4.show();
    cout << endl;

    c1.add(c2);
    cout << "c1 += c2, " << "c1 = ";
    c1.show();
    cout << endl;
}

任务4 源代码：

User.hpp

#pragma once
#include <iostream>
#include <iomanip>

bool CheckStr(const std::string &str)
{
    const char *cstr = str.c_str();
    char *ptr = const_cast<char *>(cstr);
    while(*ptr != '\0')
    {
        if(*ptr > '0' && *ptr < '9')
            ptr++;
        else
            return false;
    }
    return true;
}

class User
{
public:
    User(const std::string &name, const std::string &passwd = "111111", const std::string &email = "") : name{name}, passwd{passwd}, email{email} { this->total_user++; }
    ~User() = default;
    static void print_n() { std::cout << "there arr " << User::total_user << " users."; }
    void set_email();
    void change_passwd();
    void print_info() const;

private:
    std::string name;
    std::string passwd;
    std::string email;
    static int total_user;
};

int User::total_user = 0;

void User::set_email()
{
    std::string tmp_email;
    while(true)
    {
        std::cout << "Enter email address: ";
        std::cin >> tmp_email;
        if(tmp_email.find('@') < tmp_email.size() && tmp_email.find(".com") < tmp_email.size())
        {
            std::cout << "email is set successfully..." << std::endl;
            this->email = tmp_email;
            return;
        }   
        else
            std::cout << "your email address is illegal..." << std::endl;
    }
}
void User::change_passwd()
{
    std::string input_passwd;
    int attempts = 3;
    std::cout << "Enter old password: ";
    std::cin >> input_passwd;
    while(--attempts)
    {
        if(input_passwd.compare(this->passwd))
        {
            std::cout << "password input error. Please re-enter again: ";
            std::cin >> input_passwd;
        }
        else
        {
            while(true)
            {
                std::string new_passwd;
                std::cout << "Enter new passwd: ";
                std::cin >> new_passwd;
                if(new_passwd.size() == 6 && CheckStr(new_passwd))
                {
                    this->passwd = new_passwd;
                    return;
                }
                else
                    std::cout << "the input contains invalid characters or the length is less than or more than six characters..." << std::endl;
            }
        }
    }
    std::cout << "Please try after a while. " << std::endl;
}
void User::print_info() const
{
    using namespace std;
    cout.width(8);
    cout << setiosflags(ios::left) << "name: ";
    cout<< this->name << endl;
    cout.width(8);
    cout << setiosflags(ios::left) << "passwd: ";
    cout << "******" << endl;
    cout.width(8);
    cout << setiosflags(ios::left) << "email: ";
    cout << this->email << endl;
}

task4.cpp

#include "User.hpp"
#include <iostream>

int main()
{
    using namespace std;

    cout << "testing 1......" << endl;
    User user1("Jonny", "92197", "xyz@hotmail.com");
    user1.print_info();

    cout << endl
         << "testing 2......" << endl
         << endl;
    User user2("Leonard");
    user2.change_passwd();
    user2.set_email();
    user2.print_info();

    cout << endl
         << "testing 3......" << endl
         << endl;
    User user3("Ricky", "123456");
    user3.set_email();
    user3.change_passwd();
    user3.print_info();

    User::print_n();
}