task3

//Complex.hpp

#ifndef COMPLEX_HPP
#define COMPLEX_HPP

#include <iostream>
#include <cmath>

using namespace std;

class Complex
{
public:
    Complex(double real0 = 0,double imag0 = 0):real{real0},imag{imag0}{};
    Complex(const Complex &c):real{c.real},imag{c.imag}{};
    double get_real() const{return real;}
    double get_imag() const{return imag;}
    void show() const;
    void add(const Complex &c);
    friend Complex add(const Complex &c1,const Complex &c2);
    friend bool is_equal(const Complex &c1,const Complex &c2);
    friend double abs(const Complex &c);
private:
    double real;
    double imag;
};

//输出复数
void Complex::show () const
{
    if(imag < 0)
    {
        cout << real << " - " << fabs(imag) << "i \n" << endl;

    }
    else if( imag == 0)
    {
        cout << real << endl;

    }
    else
    {
    cout << real << " + " << imag << "i \n" << endl;
    }
} 

//把一个复数加到自身 
void Complex::add(const Complex &c) 
{
    real += c.real; 
    imag += c.imag;
}

//友元函数add
Complex add(const Complex &c1,const Complex &c2)
{
    Complex c;
    c.real = c1.real + c2.real;
    c.imag = c1.imag + c2.imag;
    return c;
}

//友元函数：判断两个复数是否相等
bool is_equal(const Complex &c1,const Complex &c2)
{
    if(c1.real == c2.real && c1.imag == c2.imag) 
        return true;
    else 
        return false;    
}

//友元函数:复数取模 
double abs(const Complex &c)
{
    return sqrt(pow(c.real,2) + pow(c.imag,2));
}

#endif 

//main.cpp

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

int main()
{
    using namespace std;

    Complex c1(6, -8);
    const Complex c2(4.1);
    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;
}

（输出有点丑懒得改了 

task4

//User.hpp

#ifndef USER_HPP
#define USER_HPP

#include<iostream>
#include<string>
using namespace std;

class User{
public:
    User(string m,string p = "111111",string e = ""):name{m},password{p},email{e}{n++;}
    User(User &u):name{u.name},password{u.password},email{u.email}{n++;}
    void set_email();
    void change_passwd();
    void print_info();
    static void print_n(){
        cout << n << endl;
    }
    ~User() {n--;}
private:
    string name;
    string password;
    string email;
    static int n;//记录用户总数 
};

int User::n = 0;

void User::set_email()
{
    cout << "请输入邮箱 " << endl; ;
    cin>>email;
}

void User::change_passwd()
{
    string p1,p2,p3;//第n次输入的密码 
    cout << "请输入旧密码" << endl;

    cin >> p1;
    string newpassword;
    
    if( p1 != password)
    {
        std::cout << "密码错误，重新输入" << std::endl;
        cin >> p2;
        if( p2 != password)
        {
            std::cout << "密码错误，重新输入" << std::endl;
            cin >> p3;
            if( p3 != password)
            {
                std::cout << "连续三次输入错误，请稍后再试" << std::endl;
            }
            else//第三次输入正确 
            {
                cout << "请输入新密码 " << endl;; 
                cin >> newpassword;
                password = newpassword;
            }
         } 
         else//第二次输入正确 
        {
            cout << "请输入新密码 " << endl ; 
            cin >> newpassword;
            password = newpassword;
        }
    }
    else//第一次输入正确 
    {                
        cout << "请输入新密码" << endl; ; 
        cin >> newpassword;
        password = newpassword;
    }
}

void User::print_info()
{
    std::cout << "name       " << name << std::endl;
    std::cout << "password   ******" << std::endl;
    std::cout << "email      " << email << std::endl;
}



#endif 

//main.cpp

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

int main()
{
using namespace std;

cout << "testing 1......" << endl;
User user1("Jiajia", "123456", "xyz@hotmail.com");
user1.print_info();

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

User::print_n();
}

实验总结：