实验4

实验1

GradeCalc.hpp

#include <algorithm>
#include <array>
#include <cstdlib>
#include <iomanip>
#include <iostream>
#include <numeric>
#include <string>
#include <vector>

#include "GradeCalc.hpp"

GradeCalc::GradeCalc(const std::string &cname):course_name{cname},is_dirty{true} {
    counts.fill(0);
    rates.fill(0);   
}

void GradeCalc::input(int n) {
    if(n < 0) {
        std::cerr << "无效输入! 人数不能为负数\n";
        std::exit(1);
    }

    grades.reserve(n);

    int grade;

    for(int i = 0; i < n;) {
        std::cin >> grade;

        if(grade < 0 || grade > 100) {
            std::cerr << "无效输入! 分数须在[0,100]\n";
            continue;
        }
        
        grades.push_back(grade);
        ++i;
    }

    is_dirty = true;  // 设置脏标记：成绩信息有变更
}

void GradeCalc::output() const {
    for(auto grade: grades)
        std::cout << grade << ' ';
    std::cout << std::endl;
}
    
void GradeCalc::sort(bool ascending) {
    if(ascending)
        std::sort(grades.begin(), grades.end());
    else
        std::sort(grades.begin(), grades.end(), std::greater<int>());
}

int GradeCalc::min() const {
    if(grades.empty())
        return -1;

    auto it = std::min_element(grades.begin(), grades.end());
    return *it;
}

int GradeCalc::max() const {
    if(grades.empty()) 
        return -1;

    auto it = std::max_element(grades.begin(), grades.end());
    return *it;
}

double GradeCalc::average() const {
    if(grades.empty())
        return 0.0;

    double avg = std::accumulate(grades.begin(), grades.end(), 0.0)/grades.size();
    return avg;
}

void GradeCalc::info() {
    if(is_dirty) 
       compute();

    std::cout << "课程名称:\t" << course_name << std::endl;
    std::cout << "平均分:\t" << std::fixed << std::setprecision(2) << average() << std::endl;
    std::cout << "最高分:\t" << max() << std::endl;
    std::cout << "最低分:\t" << min() << std::endl;

    const std::array<std::string, 5> grade_range{"[0, 60) ", 
                                           "[60, 70)", 
                                           "[70, 80)",
                                           "[80, 90)", 
                                           "[90, 100]"};
    
    for(int i = static_cast<int>(grade_range.size())-1; i >= 0; --i)
        std::cout << grade_range[i] << "\t: " << counts[i] << "人\t"
                  << std::fixed << std::setprecision(2) << rates[i]*100 << "%\n";
}

void GradeCalc::compute() {
    if(grades.empty())
        return;

    counts.fill(0); 
    rates.fill(0.0);

    // 统计各分数段人数
    for(auto grade:grades) {
        if(grade < 60)
            ++counts[0];        // [0, 60)
        else if (grade < 70)
            ++counts[1];        // [60, 70)
        else if (grade < 80)
            ++counts[2];        // [70, 80)
        else if (grade < 90)
            ++counts[3];        // [80, 90)
        else
            ++counts[4];        // [90, 100]
    }

    // 统计各分数段比例
    for(size_t i = 0; i < rates.size(); ++i)
        rates[i] = counts[i] * 1.0 / grades.size();
    
    is_dirty = false;  // 更新脏标记
}

GradeCalc.hpp

#pragma once

#include <vector>
#include <array>
#include <string>

class GradeCalc {
public:
    GradeCalc(const std::string &cname);      
    void input(int n);                         // 录入n个成绩
    void output() const;                      // 输出成绩
    void sort(bool ascending = false);        // 排序 (默认降序)
    int min() const;                          // 返回最低分（如成绩未录入，返回-1)
    int max() const;                          // 返回最高分 （如成绩未录入，返回-1)
    double average() const;                   // 返回平均分 （如成绩未录入，返回0.0)
    void info();                      // 输出课程成绩信息 

private:
    void compute();     // 成绩统计

private:
    std::string course_name;     // 课程名
    std::vector<int> grades;     // 课程成绩
    std::array<int, 5> counts;      // 保存各分数段人数（[0, 60), [60, 70), [70, 80), [80, 90), [90, 100]
    std::array<double, 5> rates;    // 保存各分数段人数占比 
    bool is_dirty;      // 脏标记，记录是否成绩信息有变更
};

task1.cpp

#include <iostream>
#include <string>
#include "GradeCalc.hpp"

void test() {
    GradeCalc c1("OOP");

    std::cout << "录入成绩:\n";
    c1.input(5);

    std::cout << "输出成绩:\n";
    c1.output();

    std::cout << "排序后成绩:\n";
    c1.sort(); c1.output();

    std::cout << "*************成绩统计信息*************\n";
    c1.info();

}

int main() {
    test();
}

问题1

std::string course_name;  储存课程名称
std::vector grades; 功能：存储所有学生的成绩
std::array<int, 5> counts; 存储5个分数段的人数统计
std::array<double, 5>; 存储5个分数段的百分比。

问题2

不合法 push_back是私有，无法访问

问题3

1次。记录是否成绩信息有变更

问题4

在info里面加。

double median() const {
    if (grades.empty()) return 0.0;
    std::vector<int> sorted = grades;
    std::sort(sorted.begin(), sorted.end());
    int n = sorted.size();
    if (n % 2 == 1)
        return sorted[n/2];
    else
        return (sorted[n/2 - 1] + sorted[n/2]) / 2.0;
}

问题5 

不能去掉。当多次调用 compute() 且成绩列表长度不变时。

问题6

对功能没有影响，对性能有影响。

 

实验2

GradeCalc.cpp

#include <algorithm>
#include <array>
#include <cstdlib>
#include <iomanip>
#include <iostream>
#include <numeric>
#include <string>
#include <vector>
#include "GradeCalc.hpp"


GradeCalc::GradeCalc(const std::string &cname): course_name{cname}, is_dirty{true}{
    counts.fill(0);
    rates.fill(0);
}   

void GradeCalc::input(int n) {
    if(n < 0) {
        std::cerr << "无效输入! 人数不能为负数\n";
        return;
    }

    this->reserve(n);

    int grade;

    for(int i = 0; i < n;) {
        std::cin >> grade;
        if(grade < 0 || grade > 100) {
            std::cerr << "无效输入! 分数须在[0,100]\n";
            continue;
        }

        this->push_back(grade);
        ++i;
    } 

    is_dirty = true;
}  

void GradeCalc::output() const {
    for(auto grade: *this)
        std::cout << grade << ' ';
    std::cout << std::endl;
} 

void GradeCalc::sort(bool ascending) {
    if(ascending)
        std::sort(this->begin(), this->end());
    else
        std::sort(this->begin(), this->end(), std::greater<int>());
}  

int GradeCalc::min() const {
    if(this->empty())
        return -1;

    return *std::min_element(this->begin(), this->end());
}  

int GradeCalc::max() const {
    if(this->empty())
        return -1;

    return *std::max_element(this->begin(), this->end());
}    

double GradeCalc::average() const {
    if(this->empty())
        return 0.0;

    double avg = std::accumulate(this->begin(), this->end(), 0.0) / this->size();
    return avg;
}   

void GradeCalc::info() {
    if(is_dirty) 
        compute();

    std::cout << "课程名称:\t" << course_name << std::endl;
    std::cout << "平均分:\t" << std::fixed << std::setprecision(2) << average() << std::endl;
    std::cout << "最高分:\t" << max() << std::endl;
    std::cout << "最低分:\t" << min() << std::endl;

    const std::array<std::string, 5> grade_range{"[0, 60) ", 
                                           "[60, 70)", 
                                           "[70, 80)",
                                           "[80, 90)", 
                                           "[90, 100]"};
    
    for(int i = static_cast<int>(grade_range.size())-1; i >= 0; --i)
        std::cout << grade_range[i] << "\t: " << counts[i] << "人\t"
                  << std::fixed << std::setprecision(2) << rates[i]*100 << "%\n";
}

void GradeCalc::compute() {
    if(this->empty())
        return;
    
    counts.fill(0);
    rates.fill(0);

    // 统计各分数段人数
    for(int grade: *this) {
        if(grade < 60)
            ++counts[0];        // [0, 60)
        else if (grade < 70)
            ++counts[1];        // [60, 70)
        else if (grade < 80)
            ++counts[2];        // [70, 80)
        else if (grade < 90)
            ++counts[3];        // [80, 90)
        else
            ++counts[4];        // [90, 100]
    }

    // 统计各分数段比例
    for(size_t i = 0; i < rates.size(); ++i)
        rates[i] = counts[i] * 1.0 / this->size();
    
    is_dirty = false;
}

 

GradeCalc.hpp

#pragma once

#include <array>
#include <string>
#include <vector>

class GradeCalc: private std::vector<int> {
public:
    GradeCalc(const std::string &cname);      
    void input(int n);                        // 录入n个成绩
    void output() const;                      // 输出成绩
    void sort(bool ascending = false);        // 排序 (默认降序)
    int min() const;                          // 返回最低分
    int max() const;                          // 返回最高分
    double average() const;                   // 返回平均分
    void info();                              // 输出成绩统计信息 

private:
    void compute();               // 计算成绩统计信息

private:
    std::string course_name;     // 课程名
    std::array<int, 5> counts;   // 保存各分数段人数（[0, 60), [60, 70), [70, 80), [80, 90), [90, 100]
    std::array<double, 5> rates; // 保存各分数段占比
    bool is_dirty;      // 脏标记，记录是否成绩信息有变更
};

task2.cpp

#include <iostream>
#include <string>
#include "GradeCalc.hpp"

void test() {
    GradeCalc c1("OOP");

    std::cout << "录入成绩:\n";
    c1.input(5);

    std::cout << "输出成绩:\n";
    c1.output();

    std::cout << "排序后成绩:\n";
    c1.sort(); c1.output();

    std::cout << "*************成绩统计信息*************\n";
    c1.info();

}

int main() {
    test();
}

问题1

  class GradeCalc: private std::vector<int> {

问题2

不能。private 继承会将基类的成员变为 private，外部无法直接调用 push_back

问题3

前者通过grade访问 后者通过this指针。

问题4

组合。组合封装性更好，且继承会增加维护难度。

实验3

Graph.cpp

#include <algorithm>
#include <cctype>
#include <iostream>
#include <string>

#include "Graph.hpp"

// Circle类实现
void Circle::draw()     { std::cout << "draw a circle...\n"; }

// Triangle类实现
void Triangle::draw()   { std::cout << "draw a triangle...\n"; }

// Rectangle类实现
void Rectangle::draw()  { std::cout << "draw a rectangle...\n"; }

// Canvas类实现
void Canvas::add(const std::string& type) {
    Graph* g = make_graph(type);
    if (g) 
        graphs.push_back(g);
}

void Canvas::paint() const {
    for (Graph* g : graphs) 
        g->draw();   
}

Canvas::~Canvas() {
    for (Graph* g : graphs) 
        delete g;
}

// 工具函数实现
// 字符串 → 枚举转换
GraphType str_to_GraphType(const std::string& s) {
    std::string t = s;
    std::transform(s.begin(), s.end(), t.begin(),
                   [](unsigned char c) { return std::tolower(c);});

    if (t == "circle")   
        return GraphType::circle;

    if (t == "triangle") 
        return GraphType::triangle;

    if (t == "rectangle")
        return GraphType::rectangle;

    return GraphType::circle;   // 缺省返回
}

// 创建图形，返回堆对象指针
Graph* make_graph(const std::string& type) {
    switch (str_to_GraphType(type)) {
    case GraphType::circle:     return new Circle;
    case GraphType::triangle:   return new Triangle;
    case GraphType::rectangle:  return new Rectangle;
    default: return nullptr;
    }
}

Graph.hpp

#pragma once

#include <string>
#include <vector>

enum class GraphType {circle, triangle, rectangle};

// Graph类定义
class Graph {
public:
    virtual void draw() {}
    virtual ~Graph() = default;
};

// Circle类声明
class Circle : public Graph {
public:
    void draw();
};

// Triangle类声明
class Triangle : public Graph {
public:
    void draw();
};

// Rectangle类声明
class Rectangle : public Graph {
public:
    void draw();
};

// Canvas类声明
class Canvas {
public:
    void add(const std::string& type);   // 根据字符串添加图形
    void paint() const;                  // 使用统一接口绘制所有图形
    ~Canvas();                           // 手动释放资源

private:
    std::vector<Graph*> graphs;          
};

// 4. 工具函数
GraphType str_to_GraphType(const std::string& s);  // 字符串转枚举类型
Graph* make_graph(const std::string& type);  // 创建图形，返回堆对象指针

task3.cpp

#include <string>
#include "Graph.hpp"

void test() {
    Canvas canvas;

    canvas.add("circle");
    canvas.add("triangle");
    canvas.add("rectangle");
    canvas.paint();
}

int main() {
    test();
}

问题1 
组合std::vector<Graph*> graphs;
继承class Circle : public Graph; class Triangle : public Graph; class Rectangle : public Graph;

问题2
 （1)会直接基类输出
  (2)导致对象切片，多态失效，无法正确调用子类 draw()
  (3)不声明虚析构函数会导致删除基类指针时子类析构函数不被调用，可能资源泄漏。

问题3
  Graph.hpp  在 enum class GraphType 中添加 star  
             声明新类 class Star : public Graph { public: void draw(); };
  Graph.cpp  实现 void Star::draw() { std::cout << "draw a star...\n"; } 
             在 str_to_GraphType 函数中增加 if (t == "star") return GraphType::star;
             在 make_graph 的 switch 语句中增加 case GraphType::star: return new Star;


问题4
make_graph 返回的对象在 Canvas 的析构函数中被释放：
cpp
Canvas::~Canvas() {
    for (Graph* g : graphs) 
        delete g;
}
（2）控制灵活，性能开销小,但是需手动释放内存。
实验4
head.cpp

#include "head.hpp"

void Toy::showname() {
    cout<<"名称: "<<name<<endl;
}

void Toy::showtype() {
    cout<<"类型: "<<type<<endl;
}

void Toy::showcolour() {
    cout<<"颜色: "<<colour<<endl;
}

void Toy::getinfo(string a, string b, string c) {
    name=a;
    type=b;
    colour=c;
}

void Toy::showAllInfo() {
    showname();
    showtype();
    showcolour();
}

void ToyFactory::addToy(Toy toy) {
    toys.push_back(toy);
}

void ToyFactory::showtoy() {
    cout<<"工厂所有玩具:" <<endl;
    for (int i=0;i<toys.size();i++) {
        cout<<"玩具"<<i+1<< ":"<<endl;
        toys[i].showAllInfo();
        cout << endl;
    }
}

void ToyFactory::showpower() {
    cout<<"玩具功能演示:"<<endl;
    for (int i=0;i<toys.size();i++) {
        cout<<toys[i].name<<"能";
        if (toys[i].type =="玩偶熊")
            cout<<"唱歌"<<endl;
        else if (toys[i].type=="玩偶兔")
            cout<<"发光"<<endl;
        else
            cout<<"运动"<<endl;
    }
}

head.cpp

#ifndef HEAD_HPP
#define HEAD_HPP

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

class Toy {
public:
    string name;
    string type;
    string colour;
    
    void showname();
    void showtype();
    void showcolour();
    void getinfo(string a, string b, string c);
    void showAllInfo();
};

class ToyFactory {
private:
    vector<Toy> toys;  
    
public:
    void addToy(Toy toy);
    void showtoy();
    void showpower();
};

#endif

demo4.cpp

#include "head.hpp"
void test() {
    Toy t1, t2, t3;
    t1.getinfo("熊", "玩偶熊", "黄色");
    t2.getinfo("兔", "玩偶兔", "白色");
    t3.getinfo("车", "塑料玩具", "红色");
    ToyFactory factory;
    factory.addToy(t1);
    factory.addToy(t2);
    factory.addToy(t3);
    factory.showtoy();
    cout << "\n";
    factory.showpower();
}

int main() {
    test();
    return 0;
}