实验2

任务1：

#include "T.h"
 #include <iostream>
 void test_T();
 int main() {
 std::cout << "test Class T: \n";
 test_T();
 
 std::cout << "\ntest friend func: \n";
 func();
}
 void test_T() {
 using std::cout;
 using std::endl;
 cout << "T info: " << T::doc << endl;
 cout << "T objects'max count: " << T::max_cnt << endl;
 cout << "T objects'current count: " << T::get_cnt() << endl << endl;
 T t1;
 cout << "t1 = "; t1.display(); cout << endl;
 T t2(3, 4);
 cout << "t2 = "; t2.display(); cout << endl;
 T t3(t2);
 t3.adjust(2);
 cout << "t3 = "; t3.display(); cout << endl;
 T t4(std::move(t2));
 cout << "t4 = "; t4.display(); cout << endl;
 cout << "test: T objects'current count: " << T::get_cnt() << endl;
 }

#include "T.h"
 #include <iostream>
 #include <string>
 // 类T实现
// static成员数据类外初始化
const std::string T::doc{"a simple class sample"};
 const int T::max_cnt = 999;
 int T::cnt = 0;
 // 类方法
int T::get_cnt() {
 return cnt;
 }
 // 对象方法

 T::T(int x, int y): m1{x}, m2{y} { 
++cnt; 
std::cout << "T constructor called.\n";
 } 
T::T(const T &t): m1{t.m1}, m2{t.m2} {
 ++cnt;
 std::cout << "T copy constructor called.\n";
 }
 T::T(T &&t): m1{t.m1}, m2{t.m2} {
 ++cnt;
 std::cout << "T move constructor called.\n";
 }    
T::~T() {--cnt;
 std::cout << "T destructor called.\n";
 }           
void T::adjust(int ratio) {
 m1 *= ratio;
 m2 *= ratio;
 }    
void T::display() const {
 std::cout << "(" << m1 << ", " << m2 << ")" ;
 }     
// 普通函数实现
void func() {
 T t5(42);
 t5.m2 = 2049;
 std::cout << "t5 = "; t5.display(); std::cout << '\n';
 }

#pragma once
 #include <string>
 // 类T: 声明

 class T {
 // 对象属性、方法
public:
 T(int x = 0, int y = 0);   // 普通构造函数
T(const T &t);  // 复制构造函数
T(T &&t);       
// 移动构造函数
~T();           
// 析构函数
void adjust(int ratio);      
void display() const;           
private:
 int m1, m2;
 // 类属性、方法
public:
 static int get_cnt();          
public:
 static const std::string doc;       
static const int max_cnt;           
private:
 static int cnt;         
// 按系数成倍调整数据
// 以(m1, m2)形式显示T类对象信息
// 显示当前T类对象总数
// 类T的描述信息
// 类T对象上限
// 当前T类对象数目
// 类T友元函数声明
friend void func();
 };
 // 普通函数声明
void func();

运行结果截图：

问题1：YES

问题2：初始化对象的成员变量并统计对象数量，创建对象时调用

 　　     用已有对象初始化新对象并统计对象数量，用一个对象初始化另一个对象时调用

  　　　 用右值对象初始化新对象并统计对象数量 用右值对象，初始化新对象时调用

　　　　减少对象数量统计，对象生命周期结束时调用

问题3：能运行

任务2：

#include "Complex.h"
 #include <iostream>
 #include <iomanip>
 #include <complex>
 void test_Complex();
 void test_std_complex();
 int main() {
 std::cout << "*******测试1: 自定义类Complex*******\n";
 test_Complex();
 std::cout << "\n*******测试2: 标准库模板类complex*******\n";
 test_std_complex();
 }
 void test_Complex() {
 using std::cout;
 using std::endl;
 using std::boolalpha;
 cout << "类成员测试: " << endl;
 cout << Complex::doc << endl << endl;
 cout << "Complex对象测试: " << endl;
 Complex c1;
 Complex c2(3, -4);
 Complex c3(c2);
 Complex c4 = c2;
 const Complex c5(3.5);

 cout << "c1 = "; output(c1); cout << endl;
 cout << "c2 = "; output(c2); cout << endl;
 cout << "c3 = "; output(c3); cout << endl;
 cout << "c4 = "; output(c4); cout << endl;
 cout << "c5.real = " << c5.get_real() 
<< ", c5.imag = " << c5.get_imag() << endl << endl;
 cout << "复数运算测试: " << endl;
 cout << "abs(c2) = " << abs(c2) << endl;
 c1.add(c2);
 cout << "c1 += c2, c1 = "; output(c1); cout << endl;
 cout << boolalpha;
 cout << "c1 == c2 : " << is_equal(c1, c2) << endl;
 cout << "c1 != c2 : " << is_not_equal(c1, c2) << endl;
 c4 = add(c2, c3);
 cout << "c4 = c2 + c3, c4 = "; output(c4); cout << endl;
 }
 void test_std_complex() {
 using std::cout;
 using std::endl;
 using std::boolalpha;
 cout << "std::complex<double>对象测试: " << endl;
 std::complex<double> c1;
 std::complex<double> c2(3, -4);
 std::complex<double> c3(c2);
 std::complex<double> c4 = c2;
 const std::complex<double> c5(3.5);
 cout << "c1 = " << c1 << endl;
 cout << "c2 = " << c2 << endl;
 cout << "c3 = " << c3 << endl;
 cout << "c4 = " << c4 << endl;
 cout << "c5.real = " << c5.real() 
<< ", c5.imag = " << c5.imag() << endl << endl;
 cout << "复数运算测试: " << endl;
 cout << "abs(c2) = " << abs(c2) << endl;
 c1 += c2;
 cout << "c1 += c2, c1 = " << c1 << endl;
 cout << boolalpha;
 cout << "c1 == c2 : " << (c1 == c2)<< endl;
 cout << "c1 != c2 : " << (c1 != c2) << endl;
 c4 = c2 + c3;
 cout << "c4 = c2 + c3, c4 = " << c4 << endl;
 }

#include "Complex.h"
#include <iostream>
#include <cmath>

using namespace std;
const string Complex::doc = "a simplified complex class";
Complex::Complex() : real(0.0), imag(0.0) {}

Complex::Complex(double r) : real(r), imag(0.0) {}

Complex::Complex(double r, double i) : real(r), imag(i) {}

Complex::Complex(const Complex& other) : real(other.real), imag(other.imag) {}


double Complex::get_real() const {
    return real;
}

double Complex::get_imag() const {
    return imag;
}

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

void output(const Complex& c) {
    cout << c.real;
    if (c.imag >= 0) {
        cout << " + " << c.imag << "i";
    } else {
        cout << " - " << -c.imag << "i";
    }
}

double abs(const Complex& c) {
    return sqrt(c.real * c.real + c.imag * c.imag);
}

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

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

bool is_not_equal(const Complex& c1, const Complex& c2) {
    return !is_equal(c1, c2);
}

#ifndef COMPLEX_H
#define COMPLEX_H
#include <string>
class Complex {
public:
    static const std::string doc;  

private:
    double real;  
    double imag; 

public:
   
    Complex();                            
    Complex(double r);                     
    Complex(double r, double i);           
    Complex(const Complex& other);        
    
   
    double get_real() const;
    double get_imag() const;
    void add(const Complex& other);
  
    friend void output(const Complex& c);
    friend double abs(const Complex& c);
    friend Complex add(const Complex& c1, const Complex& c2);
    friend bool is_equal(const Complex& c1, const Complex& c2);
    friend bool is_not_equal(const Complex& c1, const Complex& c2);
};

void output(const Complex& c);
double abs(const Complex& c);
Complex add(const Complex& c1, const Complex& c2);
bool is_equal(const Complex& c1, const Complex& c2);
bool is_not_equal(const Complex& c1, const Complex& c2);

#endif

运行结果截图：

问题1：标准库模板类complex的用法更简洁，函数和运算内在有关联，标准库通过运算符重载让复数运算更符合数学表达习惯，使代码更直观易读

问题2-1：是，output、abs、add等函数需要访问私有数据real和imag来计算或输出复数内容

问题2-2：标准库std::complex没有把abs设为友元，而是通过公有接口real()和imag()来访问数据

问题2-3：需要让外部函数直接访问类的私有成员时，实现对称的二元运算符时，需要保持封装性但又允许特定函数访问私有数据时，但应谨慎使用，优先考虑通过公有接口访问数据。

问题3：应该将拷贝构造函数声明为private或者使用=delete


任务3：

#include "PlayerControl.h"
 #include <iostream>
 #include <algorithm>   
int PlayerControl::total_cnt = 0;
 PlayerControl::PlayerControl() {}
 ControlType PlayerControl::parse(const std::string& control_str) {
    std::string lower_str = control_str;
    std::transform(lower_str.begin(), lower_str.end(), lower_str.begin(), ::tolower);
    
    ControlType result;
    if (lower_str == "play") {
        result = ControlType::Play;
    } else if (lower_str == "pause") {
        result = ControlType::Pause;
    } else if (lower_str == "next") {
        result = ControlType::Next;
    } else if (lower_str == "prev") {
        result = ControlType::Prev;
    } else if (lower_str == "stop") {
        result = ControlType::Stop;
    } else {
        result = ControlType::Unknown;
    }
    
    total_cnt++;
    return result;
 }
 void PlayerControl::execute(ControlType cmd) const {
    switch (cmd) {
    case ControlType::Play:  std::cout << "[play] Playing music...\n"; break;
    case ControlType::Pause: std::cout << "[Pause] Music paused\n";    break;
    case ControlType::Next:  std::cout << "[Next] Skipping to next track\n"; break;
    case ControlType::Prev:  std::cout << "[Prev] Back to previous track\n"; break;
    case ControlType::Stop:  std::cout << "[Stop] Music stopped\n"; break;
    default:                 std::cout << "[Error] unknown control\n"; break;
    }
 }
 int PlayerControl::get_cnt() {
    return total_cnt;
 }

#pragma once
 #include <string>
 enum class ControlType {Play, Pause, Next, Prev, Stop, Unknown};
 class PlayerControl {
 public:
 PlayerControl();
 
 static int get_cnt();
 ControlType parse(const std::string& control_str);   // 实现std::string --> ControlType转换

void execute(ControlType cmd) const;   // 执行控制操作（以打印输出模拟）       
private:
 static int total_cnt;   
};

#include "PlayerControl.h"
 #include <iostream>
 void test() {
    PlayerControl controller;
    std::string control_str;
    std::cout << "Enter Control: (play/pause/next/prev/stop/quit):\n";
    while(std::cin >> control_str) {
        if(control_str == "quit")
            break;
        
        ControlType cmd = controller.parse(control_str);
        controller.execute(cmd);
        std::cout << "Current Player control: " << PlayerControl::get_cnt() << "\n\n";
    }
    }
 int main() {
    test();
 }

运行结果截图：

任务4：

#include "Fraction.h"
#include <stdexcept>
#include <cmath>
#include <iostream>

using namespace std;

const string Fraction::doc = "Fraction类 v 0.01版。\n目前仅支持分数对象的构造、输出、加/减/乘/除运算。";

int Fraction::gcd(int a, int b) const {
    a = abs(a);
    b = abs(b);
    while (b != 0) {
        int temp = b;
        b = a % b;
        a = temp;
    }
    return a;
}

void Fraction::simplify() {
    if (down == 0) return; 
    if (down < 0) {
        up = -up;
        down = -down;
    }
    
   
    int common = gcd(up, down);
    if (common != 0) {
        up /= common;
        down /= common;
    }
}


Fraction::Fraction(int numerator, int denominator) : up(numerator), down(denominator) {
    simplify();
}

Fraction::Fraction(const Fraction& other) : up(other.up), down(other.down) {}

int Fraction::get_up() const {
    return up;
}

int Fraction::get_down() const {
    return down;
}

Fraction Fraction::negative() const {
    return Fraction(-up, down);
}

void output(const Fraction& f) {
    if (f.down == 0) {
        cout << "分母不能为0";
    } else if (f.down == 1) {
        cout << f.up;
    } else {
        cout << f.up << "/" << f.down;
    }
}

Fraction add(const Fraction& f1, const Fraction& f2) {
    int new_up = f1.up * f2.down + f2.up * f1.down;
    int new_down = f1.down * f2.down;
    return Fraction(new_up, new_down);
}

Fraction sub(const Fraction& f1, const Fraction& f2) {
    int new_up = f1.up * f2.down - f2.up * f1.down;
    int new_down = f1.down * f2.down;
    return Fraction(new_up, new_down);
}

Fraction mul(const Fraction& f1, const Fraction& f2) {
    int new_up = f1.up * f2.up;
    int new_down = f1.down * f2.down;
    return Fraction(new_up, new_down);
}

Fraction div(const Fraction& f1, const Fraction& f2) {
    if (f2.up == 0) {
       
        return Fraction(1, 0);
    }
    int new_up = f1.up * f2.down;
    int new_down = f1.down * f2.up;
    return Fraction(new_up, new_down);
}

#ifndef FRACTION_H
#define FRACTION_H

#include <string>
#include <iostream>

class Fraction {
private:
    int up;     
    int down;   
  
    int gcd(int a, int b) const;
   
    void simplify();
    
public:
    
    static const std::string doc;
  
    Fraction(int numerator = 0, int denominator = 1);
    Fraction(const Fraction& other);
    
    int get_up() const;
    int get_down() const;
    Fraction negative() const;
    
    friend void output(const Fraction& f);
    friend Fraction add(const Fraction& f1, const Fraction& f2);
    friend Fraction sub(const Fraction& f1, const Fraction& f2);
    friend Fraction mul(const Fraction& f1, const Fraction& f2);
    friend Fraction div(const Fraction& f1, const Fraction& f2);
};

void output(const Fraction& f);
Fraction add(const Fraction& f1, const Fraction& f2);
Fraction sub(const Fraction& f1, const Fraction& f2);
Fraction mul(const Fraction& f1, const Fraction& f2);
Fraction div(const Fraction& f1, const Fraction& f2);

#endif

#include "Fraction.h"
#include <iostream>

void test1();
void test2();

int main() {
    std::cout << "测试1: Fraction类基础功能测试\n";
    test1();

    std::cout << "\n测试2: 分母为0测试:\n";
    test2();
}
 void test1() {
 using std::cout;
 using std::endl;   
cout << "Fraction类测试: " << endl;
 cout << Fraction::doc << endl << endl;
 Fraction f1(5);
 Fraction f2(3, -4), f3(-18, 12);
 Fraction f4(f3);
 cout << "f1 = "; output(f1); cout << endl;
 cout << "f2 = "; output(f2); cout << endl;
 cout << "f3 = "; output(f3); cout << endl;
 cout << "f4 = "; output(f4); cout << endl;
 
   const Fraction f5(f4.negative());
    cout << "f5 = "; output(f5); cout << endl;
    cout << "f5.get_up() = " << f5.get_up()
        << ", f5.get_down() = " << f5.get_down() << endl;

    cout << "f1 + f2 = "; output(add(f1, f2)); cout << endl;
    cout << "f1 - f2 = "; output(sub(f1, f2)); cout << endl;
    cout << "f1 * f2 = "; output(mul(f1, f2)); cout << endl;
    cout << "f1 / f2 = "; output(div(f1, f2)); cout << endl;
    cout << "f4 + f5 = "; output(add(f4, f5)); cout << endl;
}

void test2() {
    using std::cout;
    using std::endl;

    Fraction f6(42, 55), f7(0, 3);

    cout << "f6 = "; output(f6); cout << endl;
    cout << "f7 = "; output(f7); cout << endl;
    cout << "f6 / f7 = "; output(div(f6, f7)); cout << endl;
}

运行结果截图：

问题：我选择的是友元函数方案

理由是，直接访问：运算函数可以直接访问分子分母，避免频繁调用getter方法。封装性：只有特定的友元函数能访问私有数据，保持了良好的封装。语法自然：add(f1, f2) 比 f1.add(f2) 更符合数学运算的对称性