c++ OOP

使用c++演示基本OOP

OOP ?

為什麼需要？我們希望機器能讀懂要做什麼，將程式碼編寫成人類行爲方便閱讀

初探OOP

其中最主要的就是纇(Class)這個物件，而在類中，定義類型為最重要的一件事
在類中有3個修飾符，分別是private,protected和public，默認為private
private外界無法訪問(黑色地帶)
protected介於private和public中間，繼承時用到(灰色地帶)
product外界可以訪問(白色地帶)

編寫代碼

#include <bits/stdc++.h>
using namespace std;
class Employee{
protected
public:
    string Name;
    string Company;
    int Age;
 
    void IntroduceYourSelf(){
        cout << "Name - " << Name  << endl;
        cout << "Company - " << Company  << endl;
        cout << "Age - " << Age  << endl;
    }
};
 
int main(int argc, const char * argv[]) {
    // insert code here...
    Employee employee;
    employee.Name = "peter";
    employee.Company = "yuntech";
    employee.Age = 18;
    employee.IntroduceYourSelf();
    return 0;
}

存在問題？

如果我們今天有100筆資料，修改繁雜且緩慢
使用構造函數(Constructors)解決

Constructors

Constructors遵守3條規則

沒有函數返回值，包括void類型定義
函數名稱和類名稱相同
請將Constructors放在public，他可以放在其他地方但很麻煩

Default Constructors

當你沒有編寫任何構造函數時，編譯器會自動編譯

編寫代碼

#include <bits/stdc++.h>
using namespace std;
class Employee{
public:
    string Name;
    string Company;
    int Age;
    void IntroduceYourSelf(){
        cout << "Name - " << Name  << endl;
        cout << "Company - " << Company  << endl;
        cout << "Age - " << Age  << endl;
    }
    Employee(string name,string company,int age){
        Name = name;
        Company = company;
        Age = age;
    }
};
 
int main(int argc, const char * argv[]) {
    // insert code here...
    Employee employee = Employee("peter","yuntech",18);
    employee.IntroduceYourSelf();
    return 0;
}

OOP最重要的事情

封裝
抽象
繼承
多態性

1.什麼是封裝

不希望其他的類可以直接對纇進行操作，將值放入private
封裝中主要使用setter和geter方法對值進行操作

#include <bits/stdc++.h>
using namespace std;
class Employee{
private:
    string Name;
    string Company;
    int Age;
public:
    void IntroduceYourSelf(){
        cout << "Name - " << Name  << endl;
        cout << "Company - " << Company  << endl;
        cout << "Age - " << Age  << endl;
    }
    void SetName(string name){
        Name = name;
    }
    void SetCompany(string company){
        Company = company;
    }
    void SetAge(int age ){
    	//Valid->當false的時候就不會設置
    	if(age >= 18)
        Age = age;
    }
    string getName(){
        return Name;
    }
    string getCompany(){
        return Company;
    }
    int getAge(){
        return Age;
    }
    Employee(string name,string company,int age){
        Name = name;
        Company = company;
        Age = age;
    }
};
 
int main(int argc, const char * argv[]) {
    // insert code here...
    Employee employee = Employee("peter","yuntech",0);
    employee.IntroduceYourSelf();
    employee.SetAge(18);
    cout << employee.getAge() << endl;
    return 0;
}

2.抽象的概念？

當你有像很複雜的產品不希望被人知道他複雜的地方
所有繼承了抽象的類都必須實現抽象的方法(虛函數)

 
#include <bits/stdc++.h>
using namespace std;
 
class iEmployee{
    virtual void AskPromotion() = 0;
};
class Employee:iEmployee{
private:
    string Name;
    string Company;
    int Age;
public:
    void IntroduceYourSelf(){
        cout << "Name - " << Name  << endl;
        cout << "Company - " << Company  << endl;
        cout << "Age - " << Age  << endl;
    }
    void SetName(string name){
        Name = name;
    }
    void SetCompany(string company){
        Company = company;
    }
    void SetAge(int age ){
        //Valid->當false的時候就不會設置
        if(age >= 18)
            Age = age;
    }
    string getName(){
        return Name;
    }
    string getCompany(){
        return Company;
    }
    int getAge(){
        return Age;
    }
    Employee(string name,string company,int age){
        Name = name;
        Company = company;
        Age = age;
    }
 
    void AskPromotion() {
        if(Age > 30)
            cout << "You can promote" << Age << endl;
        else
            cout << "You can not promote" << Age << endl;
    }
};
 
int main(int argc, const char * argv[]) {
    // insert code here...
    Employee employee = Employee("peter","yuntech",18);
    Employee employee2 = Employee("james","yuntech",40);
    employee.AskPromotion();
    employee2.AskPromotion();
 
    return 0;
}

3.繼承

希望後續的class能擁有其父元素的屬性

#include <bits/stdc++.h>
using namespace std;
 
class iEmployee{
    virtual void AskPromotion() = 0;
};
class Employee:iEmployee{
private:
    string Name;
    string Company;
    int Age;
public:
    void IntroduceYourSelf(){
        cout << "Name - " << Name  << endl;
        cout << "Company - " << Company  << endl;
        cout << "Age - " << Age  << endl;
    }
    void SetName(string name){
        Name = name;
    }
    void SetCompany(string company){
        Company = company;
    }
    void SetAge(int age ){
        //Valid->當false的時候就不會設置
        if(age >= 18)
            Age = age;
    }
    string getName(){
        return Name;
    }
    string getCompany(){
        return Company;
    }
    int getAge(){
        return Age;
    }
    Employee(string name,string company,int age){
        Name = name;
        Company = company;
        Age = age;
    }
 
    void AskPromotion() {
        if(Age > 30)
            cout << "You can promote" << Age << endl;
        else
            cout << "You can not promote" << Age << endl;
    }
};
 
class Developer:Employee {
public:
    string FavProgrammingLanguage ;
    Developer(string Name,string Company,int Age,string favProgrammingLanguage)
    : Employee(Name,Company,Age)
    {
        FavProgrammingLanguage = favProgrammingLanguage;
    }
    void fixBug(){
        cout << getName() << " fix " << FavProgrammingLanguage << " problem " << endl;
    }
};
int main(int argc, const char * argv[]) {
    // insert code here...
    Developer d = Developer("peter","yuntech",18,"golang");
    d.fixBug();
    return 0;
}

發現問題！

我們有沒有辦法不要透過getName()來獲得父類別的元素

解決：使用protected修飾符號

沒有辦法獲得父類別的所有屬性，包括抽象函數

解決：繼承時將父類別設為public

#include <bits/stdc++.h>
using namespace std;
 
class iEmployee{
    virtual void AskPromotion() = 0;
};
class Employee:iEmployee{
protected:
    string Name;
    string Company;
    int Age;
public:
    void IntroduceYourSelf(){
        cout << "Name - " << Name  << endl;
        cout << "Company - " << Company  << endl;
        cout << "Age - " << Age  << endl;
    }
    void SetName(string name){
        Name = name;
    }
    void SetCompany(string company){
        Company = company;
    }
    void SetAge(int age ){
        //Valid->當false的時候就不會設置
        if(age >= 18)
            Age = age;
    }
    string getName(){
        return Name;
    }
    string getCompany(){
        return Company;
    }
    int getAge(){
        return Age;
    }
    Employee(string name,string company,int age){
        Name = name;
        Company = company;
        Age = age;
    }
    void AskPromotion() {
        if(Age > 30)
            cout << "You can promote " << Name << endl;
        else
            cout << "You can not promote " << Name << endl;
    }
};
 
class Developer:public Employee {
public:
    string FavProgrammingLanguage ;
    Developer(string Name,string Company,int Age,string favProgrammingLanguage)
    : Employee(Name,Company,Age)
    {
        FavProgrammingLanguage = favProgrammingLanguage;
    }
    void fixBug(){
        cout << Name << " fix " << FavProgrammingLanguage << " problem " << endl;
    }
};
int main(int argc, const char * argv[]) {
    // insert code here...
    Developer d = Developer("peter","yuntech",18,"golang");
    d.fixBug();
    d.AskPromotion();
    return 0;
}

4.多態性

#include <bits/stdc++.h>
using namespace std;
 
class iEmployee{
    virtual void AskPromotion() = 0;
};
class Employee:iEmployee{
protected:
    string Name;
    string Company;
    int Age;
public:
    void IntroduceYourSelf(){
        cout << "Name - " << Name  << endl;
        cout << "Company - " << Company  << endl;
        cout << "Age - " << Age  << endl;
    }
    void SetName(string name){
        Name = name;
    }
    void SetCompany(string company){
        Company = company;
    }
    void SetAge(int age ){
        //Valid->當false的時候就不會設置
        if(age >= 18)
            Age = age;
    }
    string getName(){
        return Name;
    }
    string getCompany(){
        return Company;
    }
    int getAge(){
        return Age;
    }
    Employee(string name,string company,int age){
        Name = name;
        Company = company;
        Age = age;
    }
    void AskPromotion() {
        if(Age > 30)
            cout << "You can promote " << Name << endl;
        else
            cout << "You can not promote " << Name << endl;
    }
    void Work(){
        cout << Name << " checking email " << endl;
    }
};
 
class Developer:public Employee {
public:
    string FavProgrammingLanguage ;
    Developer(string Name,string Company,int Age,string favProgrammingLanguage)
    : Employee(Name,Company,Age)
    {
        FavProgrammingLanguage = favProgrammingLanguage;
    }
    void fixBug(){
        cout << Name << " fix " << FavProgrammingLanguage << " problem " << endl;
    }
    void Work(){
        cout << Name << " coding " << endl;
    }
};
 
class Teacher: public Employee{
public:
    string Subject;
    Teacher(string Name,string Company,int Age,string subject)
    : Employee(Name,Company,Age)
    {
        Subject = subject;
    }
    void Prepare(){
        cout << Name << " preparing " << Subject;
    }
    void Work(){
        cout << Name << " tech knowledge " << endl;
    }
};
int main(int argc, const char * argv[]) {
    // insert code here...
    Developer d = Developer("peter","yuntech",18,"golang");
    Teacher t = Teacher("james","yuntech",70,"history");
    d.Work();
    t.Work();
    return 0;
}

多態性常用方法

直接使用父類別完成子類別的各種方法
- 遇到還是使用父類別的方法時，可以使用虛擬函數來解決
為什麼虛擬函數可以解決？
- 虛擬函數會去檢查最底層的繼承者有沒有使用虛擬函數，如果有的話就使用

#include <bits/stdc++.h>
using namespace std;
 
class iEmployee{
    virtual void AskPromotion() = 0;
};
class Employee:iEmployee{
protected:
    string Name;
    string Company;
    int Age;
public:
    void IntroduceYourSelf(){
        cout << "Name - " << Name  << endl;
        cout << "Company - " << Company  << endl;
        cout << "Age - " << Age  << endl;
    }
    void SetName(string name){
        Name = name;
    }
    void SetCompany(string company){
        Company = company;
    }
    void SetAge(int age ){
        //Valid->當false的時候就不會設置
        if(age >= 18)
            Age = age;
    }
    string getName(){
        return Name;
    }
    string getCompany(){
        return Company;
    }
    int getAge(){
        return Age;
    }
    Employee(string name,string company,int age){
        Name = name;
        Company = company;
        Age = age;
    }
    void AskPromotion() {
        if(Age > 30)
            cout << "You can promote " << Name << endl;
        else
            cout << "You can not promote " << Name << endl;
    }
    virtual void Work(){
        cout << Name << " checking email " << endl;
    }
};
 
class Developer:public Employee {
public:
    string FavProgrammingLanguage ;
    Developer(string Name,string Company,int Age,string favProgrammingLanguage)
    : Employee(Name,Company,Age)
    {
        FavProgrammingLanguage = favProgrammingLanguage;
    }
    void fixBug(){
        cout << Name << " fix " << FavProgrammingLanguage << " problem " << endl;
    }
    void Work(){
        cout << Name << " coding " << endl;
    }
};
 
class Teacher: public Employee{
public:
    string Subject;
    Teacher(string Name,string Company,int Age,string subject)
    : Employee(Name,Company,Age)
    {
        Subject = subject;
    }
    void Prepare(){
        cout << Name << " preparing " << Subject;
    }
    void Work(){
        cout << Name << " tech knowledge " << endl;
    }
};
int main(int argc, const char * argv[]) {
    // insert code here...
    Developer d = Developer("peter","yuntech",18,"golang");
    Teacher t = Teacher("james","yuntech",70,"history");
    Employee* e1 = &d;
    Employee* e2 = &t;
    e1->Work();
    e2->Work();
    return 0;
}

Friend類

當我需要可以使用其他類別的private時，直接引入發現因為private而不可訪問
- 解決：將要調用的類設為friend class

#include <bits/stdc++.h>
 
using namespace std;
 
class Home {
private:
    string Name;
public:
    Home(string name){
        Name = name;
    }
    void member(){
        cout << Name << " in home" << endl;
    }
    friend class Get;
};
 
class Get{
private:
    string Name;
public:
    Get(string name){
        Name = name;
    }
    void ISHe(Home  h,Get g){
        if (h.Name == h.Name)
            cout << "YES" << endl;
        else
            cout << "NO" << endl;
    }
};
 
int main(){
    Home h = Home("peter");
    h.member();
    Get g = Get("peter");
    g.ISHe(h,g);
}

運算子多載

多載運算子的名稱是 operatorx，其中x是下表中顯示的運算子。例如，若要多載加運算子，您可以定義稱為 operator+的函式。
為什麼要運算子多載？
- 當成員元素為private時，只要一多就會需要大量get和set相加，使用運算子多載可以避免這種狀況
如何決定運算子參數數量？
使用運算子多載以外需要運算的類別

希望實現n1+n2

#include <bits/stdc++.h>
using namespace std;
 
class Number{
private:
    int number;
public:
    Number(int num){
        number = num;
    }
 
};
 
int main(){
    Number n1 = Number(12);
    Number n2 = Number(10);
}

解決

#include <bits/stdc++.h>
using namespace std;
 
class Number{
private:
    int number;
public:
    Number(int num){
        number = num;
    }
    Number operator+(Number &n2){
        return number + n2.number;
    };
    int getNumber(){
        return number;
    }
};
 
int main(){
    Number n1 = Number(12);
    Number n2 = Number(10);
    Number n3 = n1+n2;
    cout << n3.getNumber() << endl;
}

Static和extern

static能夠讓指定變數跳脫做用域
extern可以讓變數再不同文件傳輸，宣告了extern的變數等同於在這個文件裡面有一個變數可以用，但是這個變數的宣告並不在此，而是有某個 include 了此文件的人會去做宣告

如果不使用static

#include <bits/stdc++.h>
using namespace std;
 
int plusNum(){
    int a =0;
    ++a;
    return a;
}
 
int main(){
    for(int i=0;i<5;i++){
        cout << plusNum() << endl;
    }
}

發現a輸出全是1
- 這時候將a設為static，a會從1加到5輸出

#include <bits/stdc++.h>
using namespace std;
 
int plusNum(){
    static int a =0;
    ++a;
    return a;
}
 
int main(){
    for(int i=0;i<5;i++){
        cout << plusNum() << endl;
    }
}

解構

程式執行完的時候自動作用

#include <bits/stdc++.h>
using namespace std;
 
 
class Test {
public:
    int number;
    Test(int num){
       number = num;
    }
    ~Test(){
        cout << "IS END" << endl;
    }
    void getNum(){
        cout << number << endl;
    }
};
int main(){
    Test t = Test(10);
    t.getNum();
    return 0;
}
 
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IS END