task3.

#ifndef  COMPLEX_HPP
#define COMPLEX_HPP 
#include<iostream>
#include<cmath>
using namespace std;
class Complex
{
    public:
        Complex(double x=0,double y=0):real(x),imag(y){}
        Complex(const Complex &c);
        ~Complex(){};
        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(Complex &c);
    private:
        double real,imag;
};

Complex::Complex(const Complex &c)
{
    real=c.real;
    imag=c.imag;
} 

void Complex::show() const
{
    if(imag==0)
        cout<<real;
    if(imag>0)
    cout<<real<<"+"<<imag<<"i";
    else if(imag<0)
    cout<<real<<imag<<"i";
}

void Complex::add(const Complex &c) 
{
    real+=c.real;
    imag+=c.imag;
}

Complex add(const Complex &c1,const Complex &c2)
{
    Complex c3;
    c3.real=c1.real+c2.real;
    c3.imag=c1.imag+c2.imag;
    return c3;
}

bool is_equal(const Complex &c1,const Complex &c2)
{
    if(c1.real==c2.real&&c1.imag==c2.imag)
        return true;
    else return false;
}

double abs(Complex &c)
{
    double x,y;
    x=c.real*c.real;
    y=c.imag*c.imag;
    return sqrt(x+y);
}

#endif

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

int main()
{
    using namespace std;

    Complex c1(3, -4);
    const Complex c2(4.5);
    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;
}

 

task4.

#ifndef USER_HPP
#define USER_HPP
#include<iostream>
#include<string>
using namespace std;
class User
{
    public:
        User(string name0,string passwd0="111111",string email0=""):name(name0),passwd(passwd0),email(email0){n++;}
        void set_email();
        void change_passwd();
        void print_info();
        static void print_n();
        ~User(){}
    private:
        string name;
        string passwd;
        string email;
        static int n;
};

int User::n=0;

void User::set_email() 
{
    cout<<"Enter email address: ";
    cin>>email;
    cout<<"email is set successfully..."<<endl;
}

void User::change_passwd() 
{
    string oldpasswd;
    int j=0;
    cout<<"Enter old password: ";
    cin>>oldpasswd;
    
    if (oldpasswd == passwd)
    {
        cout << "Enter new passwd: ";
        cin >> passwd;
    }
        
    else
    {
        
        do
        {
            j++;
            cout<<"password input error. Please re-enter again: "; 
            cin>>oldpasswd;
            if(j==2)
            {
                cout<<"password input error. Please try after a while."<<endl;
                break; 
            }
        }while(oldpasswd!=passwd);
        if(oldpasswd==passwd)
        cin>>passwd;
    }
}

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

void User::print_n()
{
    cout<<"there are "<<n<<" users."<<endl;
 } 
 
#endif

#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();

    User::print_n();
}