第9课: 面向对象基础

类与对象

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

class Student {
public:
    // 成员变量
    string name;
    int age;
    int score;

    // 成员函数
    void display() {
        cout << "姓名：" << name << endl;
        cout << "年龄：" << age << endl;
        cout << "分数：" << score << endl;
    }
};

int main() {
    // 创建对象
    Student stu1;
    stu1.name = "张三";
    stu1.age = 20;
    stu1.score = 95;

    stu1.display();

    return 0;
}

封装 - 访问权限

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

class BankAccount {
private:
    // 私有成员：只能在类内部访问
    string accountNumber;
    double balance;

public:
    // 公有成员：可以在类外部访问
    string ownerName;

    // 设置账户信息
    void setAccount(string accNum, double bal) {
        accountNumber = accNum;
        balance = bal;
    }

    // 存款
    void deposit(double amount) {
        if (amount > 0) {
            balance += amount;
            cout << "存款成功！" << endl;
        }
    }

    // 取款
    void withdraw(double amount) {
        if (amount > 0 && amount <= balance) {
            balance -= amount;
            cout << "取款成功！" << endl;
        } else {
            cout << "余额不足！" << endl;
        }
    }

    // 查询余额
    double getBalance() {
        return balance;
    }

protected:
    // 受保护成员：可以被派生类访问
    void log(string message) {
        cout << "[日志] " << message << endl;
    }
};

int main() {
    BankAccount account;
    account.ownerName = "李四";
    account.setAccount("6222021234567890", 1000.0);

    account.deposit(500);
    account.withdraw(200);
    cout << "当前余额：" << account.getBalance() << endl;

    return 0;
}

类的成员函数定义

#include <iostream>
using namespace std;

class Rectangle {
private:
    double width;
    double height;

public:
    // 类内声明
    void setDimensions(double w, double h);
    double getArea();
    double getPerimeter();
};

// 类外定义
void Rectangle::setDimensions(double w, double h) {
    width = w;
    height = h;
}

double Rectangle::getArea() {
    return width * height;
}

double Rectangle::getPerimeter() {
    return 2 * (width + height);
}

int main() {
    Rectangle rect;
    rect.setDimensions(5.0, 3.0);

    cout << "面积：" << rect.getArea() << endl;
    cout << "周长：" << rect.getPerimeter() << endl;

    return 0;
}

this指针

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

class Person {
private:
    string name;
    int age;

public:
    void setName(string name) {
        this->name = name;  // this指向当前对象
    }

    void setAge(int age) {
        this->age = age;
    }

    void display() {
        cout << "姓名：" << this->name << endl;
        cout << "年龄：" << this->age << endl;
    }

    // 返回当前对象的引用
    Person& setInfo(string name, int age) {
        this->name = name;
        this->age = age;
        return *this;
    }
};

int main() {
    Person p;
    p.setInfo("王五", 25).display();  // 链式调用

    return 0;
}

静态成员

#include <iostream>
using namespace std;

class Counter {
private:
    static int count;  // 静态成员变量

public:
    Counter() {
        count++;
    }

    static int getCount() {  // 静态成员函数
        return count;
    }
};

// 静态成员变量必须在类外初始化
int Counter::count = 0;

int main() {
    cout << "初始计数：" << Counter::getCount() << endl;

    Counter c1, c2, c3;
    cout << "创建3个对象后：" << Counter::getCount() << endl;

    return 0;
}

友元函数

#include <iostream>
using namespace std;

class Box {
private:
    double width;

public:
    Box(double w) : width(w) {}

    // 声明友元函数
    friend void printWidth(Box box);
};

// 友元函数可以访问私有成员
void printWidth(Box box) {
    cout << "宽度：" << box.width << endl;
}

int main() {
    Box box(10.5);
    printWidth(box);

    return 0;
}