实验4
实验任务一
#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 };
#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 }
#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(); }
问题一：
std::string course_name：保存课程名称
std::vector<int> grades：保存学生成绩
std::array<int, 5> counts：保存各分段的人数
std::array<double, 5> rates：保存各分段比例
问题二：
不合法，外部代码不应直接访问内部vector的接口，破坏了封装性
问题三：
（1）一次；避免重复计算
（2）不需要，需要设置is_dirty = true
问题四：
在info（）中加：
sort(true);
if(!grades.empty()) {
if(grades.size() % 2 == 1) {
median = grades[grades.size()/2];
} else {
median = (grades[grades.size()/2-1] + grades[grades.size()/2]) / 2.0;
}
}
问题五：
不能去掉，当成绩数据被清空或修改后重新统计时，旧的统计结果会残留，导致统计信息不准确
问题六：
（1）没有
（2）有，去掉reserve(n)后，vector在动态增长时需要多次重新分配内存和拷贝数据，降低程序运行效率
实验任务二
#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 };
#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; }
#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(); }
问题一：
class GradeCalc : private std::vector<int>
问题二：
不会，不能，push_back是std::vector<int>的公有成员，但因私有继承在GradeCalc中变为私有，外部不能调用
问题三：
组合把容器作为实现细节封装在成员变量中，可以更加清晰明确地使用；继承会把容器的语义和接口混入类的行为中，语义不清晰
问题四：
组合方案，组合语言更加清晰明确，便于理解，在该场景下更加方便
实验任务三
#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
#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; } }
#include <string> #include "Graph.hpp" void test() { Canvas canvas; canvas.add("circle"); canvas.add("triangle"); canvas.add("rectangle"); canvas.paint(); } int main() { test(); }
问题一：
（1）std::vector<Graph*> graphs;
（2）
class Circle : public Graph
class Triangle : public Graph
class Rectangle : public Graph
问题二：
（1）无论添加什么图形，都只会执行Graph::draw()的空实现，无法实现多态
（2）无法存储派生类对象，失去多态性
（3）导致派生类部分资源泄漏，内存管理不安全
问题三：
Graph.hpp:
enum class GraphType {circle, triangle, rectangle, star}; // 扩展枚举
class Star : public Graph { // 新增Star类声明
public:
void draw();
};
Graph.cpp:
void Star::draw() { std::cout << "draw a star...\n"; }
在str_to_GraphType函数中添加star字符串判断
在make_graph函数的switch-case中添加star分支
问题四：
（1）在Canvas::~Canvas()析构函数中被释放
（2）优点：简单直观，便于理解指针概念
缺点：容易造成内存泄漏，可能存在重复释放风险
实验任务四
#ifndef TOY_HPP #define TOY_HPP #include <string> #include <iostream> // 抽象基类：毛绒玩具 class Toy { protected: std::string name; std::string type; std::string color; double price; public: Toy(const std::string& n, const std::string& t, const std::string& c, double p); virtual ~Toy() = default; // 虚函数：特异功能接口 virtual void specialFunction() = 0; virtual void displayInfo() const; // getter方法 std::string getName() const { return name; } std::string getType() const { return type; } }; // 具体玩具类：会说话的熊 class TalkingBear : public Toy { private: std::string phrase; public: TalkingBear(const std::string& n, const std::string& p); void specialFunction() override; }; // 具体玩具类：发光兔子 class GlowingRabbit : public Toy { private: std::string lightColor; public: GlowingRabbit(const std::string& n, const std::string& lc); void specialFunction() override; }; // 具体玩具类：音乐猫 class MusicCat : public Toy { private: std::string songName; public: MusicCat(const std::string& n, const std::string& song); void specialFunction() override; }; #endif
#include "Toy.hpp" #include <iostream> // Toy基类实现 Toy::Toy(const std::string& n, const std::string& t, const std::string& c, double p) : name(n), type(t), color(c), price(p) {} void Toy::displayInfo() const { std::cout << "玩具名称: " << name << " | 类型: " << type << " | 颜色: " << color << " | 价格: ￥" << price << std::endl; } // TalkingBear实现 TalkingBear::TalkingBear(const std::string& n, const std::string& p) : Toy(n, "会说话的熊", "棕色", 99.9), phrase(p) {} void TalkingBear::specialFunction() { std::cout << name << "说: \"" << phrase << "\"" << std::endl; } // GlowingRabbit实现 GlowingRabbit::GlowingRabbit(const std::string& n, const std::string& lc) : Toy(n, "发光兔子", "白色", 79.9), lightColor(lc) {} void GlowingRabbit::specialFunction() { std::cout << name << "发出" << lightColor << "的光芒，温暖又可爱！" << std::endl; } // MusicCat实现 MusicCat::MusicCat(const std::string& n, const std::string& song) : Toy(n, "音乐猫", "灰色", 129.9), songName(song) {} void MusicCat::specialFunction() { std::cout << name << "播放歌曲: 《" << songName << "》" << std::endl; }
#ifndef TOYFACTORY_HPP #define TOYFACTORY_HPP #include "Toy.hpp" #include <vector> #include <memory> class ToyFactory { private: std::vector<std::unique_ptr<Toy>> toys; public: void addToy(std::unique_ptr<Toy> toy); void displayAllToys() const; void testAllSpecialFunctions() const; size_t getToyCount() const { return toys.size(); } }; #endif
#include "ToyFactory.hpp" #include <iostream> void ToyFactory::addToy(std::unique_ptr<Toy> toy) { toys.push_back(std::move(toy)); } void ToyFactory::displayAllToys() const { std::cout << "=== 玩具工厂库存 ===" << std::endl; for (size_t i = 0; i < toys.size(); ++i) { std::cout << i + 1 << ". "; toys[i]->displayInfo(); } std::cout << "总计: " << toys.size() << " 个玩具" << std::endl; } void ToyFactory::testAllSpecialFunctions() const { std::cout << "=== 特异功能测试 ===" << std::endl; for (size_t i = 0; i < toys.size(); ++i) { std::cout << i + 1 << ". "; toys[i]->specialFunction(); // 多态调用 } }
#define _GLIBCXX_USE_CXX11_ABI 1 #include "ToyFactory.hpp" #include <memory> int main() { ToyFactory factory; factory.addToy(std::unique_ptr<Toy>(new TalkingBear("小熊", "蜂蜜真好吃！"))); factory.addToy(std::unique_ptr<Toy>(new GlowingRabbit("小白", "粉红色"))); factory.addToy(std::unique_ptr<Toy>(new MusicCat("音乐喵", "小星星"))); factory.addToy(std::unique_ptr<Toy>(new TalkingBear("布朗熊", "你好呀！"))); factory.displayAllToys(); std::cout << std::endl; factory.testAllSpecialFunctions(); return 0; }
继承：定义抽象基类Toy，派生具体玩具类
组合：ToyFactory通过vector组合管理多个Toy对象
多态：通过虚函数实现统一接口调用特异功能
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