Использование указателя this

#include <iostream>
#include<cstring>
using namespace std;
 
class Date
{
private:
    int day;
    int month;
    int year;
public:
    Date();
    Date(int d, int m, int y);
 
    void setday(int d);
 
    int getday();
 
    void setmonth(int m);
    int getmonth();
 
    void setyear(int y);
 
    int getyear();
 
    void showdate();
    ~Date();
};
 
void Date::showdate()
{
    cout << day << "-" << month << "-" << year;
}
 
Date::~Date()
{
 
}
 
Date::Date()
{
    day = 0;
    month = 0;
    year = 0;
}
 
Date::Date(int d, int m, int y)
{
    if (d >= 1 && d <= 31 && m >= 1 && m <= 12 && y > 1990)
    {
        day = d;
        month = m;
        year = y;
    }
    else
    {
        day = 0;
        month = 0;
        year = 0;
    }
}
 
void Date::setday(int d)
{
    if (d >= 1 && d <= 31)
    {
        day = d;
    }
    else
    {
        cout << "Error\n";
    }
 
}
 
int Date::getday()
{
    return day;
}
 
void Date::setmonth(int m)
{
    if (m >= 1 && m <= 12)
    {
        month = m;
    }
    else
    {
        cout << "Error\n";
    }
 
}
 
int Date::getmonth()
{
    return month;
}
 
void Date::setyear(int y)
{
    if (y >= 0 && y <= 1990)
    {
        year = y;
    }
    else
    {
        cout << "Error\n";
    }
 
}
 
int Date::getyear()
{
    return year;
}
 
 
class User
{
private:
    char* login;
    char* password;
    char* email;
    char* secretword;
    Date birth;
 
public:
    User();
    User(const char* login = "NewUser",
        const char* password = "123456",
        const char* secretword = "people",
        const char* email = "go@cars.academy",
        int day = 1, int month = 1, int year = 1900);
 
    void setLogin(const char* login);
    char* getLogin();
 
    void setPassword(const char* password);
    char* getPassword();
 
    void setEmail(const char* email);
    char* getEmail();
    void setSecretWord(const char* secretword);
    const char* getSecretWord();
 
    void showInfo();
 
 
    ~User();
};
 
User::User()
{
    this->login = new char[strlen("Its my") + 1];
    strcpy_s(this->login, strlen("Its my") + 1, "Its my");
 
    (*this).password = new char[strlen("12345678") + 1];
    strcpy_s((*this).password, strlen("12345678") + 1, "12345678");
 
    this->email = new char[strlen("go@cars.academy") + 1];
    strcpy_s(this->email, strlen("go@mecars.academy") + 1, "go@cars.academy");
 
    this->secretword = new char[strlen("people") + 1];
    strcpy_s(this->secretword, strlen("people") + 1, "people");
 
}
 
User::User(const char* login, const char* password, const char* email, const char* secretword, int day, int month, int year)
{
    this->login = new char[strlen(login) + 1];
    strcpy_s(this->login, strlen(login) + 1, login);
 
    (*this).password = new char[strlen(password) + 1];
    strcpy_s((*this).password, strlen(password) + 1, password);
 
    this->email = new char[strlen(email) + 1];
    strcpy_s(this->email, strlen(email) + 1, email);
 
    this->secretword = new char[strlen(secretword) + 1];
    strcpy_s(this->secretword, strlen(secretword) + 1, secretword);
 
    birth = Date(day, month, year);
}
 
void User::setLogin(const char* login)
{
    if (this->login != NULL) delete[] this->login;
    this->login = new char[strlen(login) + 1];
    strcpy_s(this->login, strlen(login) + 1, login);
}
 
char* User::getLogin()
{
    return login;
}
 
void User::setPassword(const char* password)
{
    if (this->password != NULL) delete[] this->password;
    this->password = new char[strlen(password) + 1];
    strcpy_s(this->password, strlen(password) + 1, password);
}
 
char* User::getPassword()
{
    return password;
}
 
void User::setEmail(const char* email)
{
    if (this->email != NULL) delete[] this->email;
    this->email = new char[strlen(email) + 1];
    strcpy_s(this->email, strlen(email) + 1, email);
}
 
char* User::getEmail()
{
    return email;
}
 
void User::setSecretWord(const char* secretword)
{
    if (this->secretword != NULL) delete[] this->secretword;
    this->secretword = new char[strlen(secretword) + 1];
    strcpy_s(this->secretword, strlen(secretword) + 1, secretword);
}
 
const char* User::getSecretWord()
{
    return secretword;
}
 
 
void User::showInfo()
{
    cout << "\nLogin:\t" << login << endl;
    cout << "Password:\t" << password << endl;
    cout << "Email:\t" << email << endl;
    cout << "Secretword:\t" << secretword << endl;
    cout << "Birthday:\t";  birth.showdate(); cout << endl;
}
 
User::~User()
{
    delete[] login;
    delete[] email;
    delete[] password;
    delete[] secretword;
}
 
int main()
{
    setlocale(LC_ALL, "");
 
    User user0("login0", "Pass0");
    User user1("login1", "Pass1", "email1@gmail.com");
    User user2("login2", "Pass2", "email2@gmail.com", "34ppv11");
    User user3("login3", "Pass3", "email3@gmail.com", "34ppv11", 1, 12, 2019);
    cout << endl;
 
    user0.setLogin("vasya");
 
    user0.showInfo();
    
 
    cout << endl; cout << endl;
    system("pause");
}