实验四
任务一：
GradeCalc.hpp
#pragma once #include<vector> #include<array> #include<string> class GradeCalc{ public: GradeCalc(const std::string &cname); void intput(int n); void output() const; void sort(bool ascending=false); int min() const; int max() const; double average() const; void info(); private: void compute(); private: std::string course_name; std::vector<int> grades; std::array<int,5> counts; std::array<double,5> rates; bool is_dirty; };
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"; 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; } 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); for(auto grade:grades) { if(grade < 60) ++counts[0]; else if (grade < 70) ++counts[1]; else if (grade < 80) ++counts[2]; else if (grade < 90) ++counts[3]; else ++counts[4]; } for(size_t i = 0; i < rates.size(); ++i) rates[i] = counts[i] * 1.0 / grades.size(); is_dirty = false; }
Demo1.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(); }
结果：
Q1:
std::vector<int>grades 动态存储学生成绩
std::array<int,5>couts 统计人数
std::array<double,5>rates 统计5个分段的百分比
Q2：
不合法，外部代码不应该直接作用于内部代码
Q3：
1.调用1次，is_dirty标记数据避免重复使用
2.无需更改compute的调用位置
Q4：
在GradeCalc.hpp中增加：
private: double median_grade; public: double median()const;
在GradeCalc.cpp增加：
if (!grades.empty()){ std::vector<int>temp=grades; std::sort(temp.begin(),temp.end()); if(temp.size()%2==1) { median_grade=temp[temp.size()/2]; }else { median_grade=(temp[temp.size()/2-1]+temp[temp.size()/2])/2; } is_dirty=false; }
Q5：
不能去掉，若去掉调用compute（）会将新的结果加到旧的结果上
Q6：
去掉grades.reserve(n)对程序没有影响
性能影响：去掉vector会增加内存的大小
任务二：
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); void output() const; void sort(bool ascending = false); int min() const; int max() const; double average() const; void info(); private: void compute(); private: std::string course_name; std::array<int, 5> counts; std::array<double, 5> rates; bool is_dirty; };
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; }
demo2.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(); }
result：
Q1:
class GradeCalc: private std::vector<int> {
Q2:
不能编译通过，因为该继承是私有继承，基类中的所有公有成员都会变成私有无法直接访问。
Q3；
组合方式：只能通过GradeCalc提供的接口访问数据
继承方式：在类的内部可以直接访问
Q4:
组合方案更好一点；1.组合方案能通过GradeCalc的接口直接访问，2.符合优先使用组合的原则
任务3;
Graph.hpp:
#pragma once #include<string> #include<vector> enum class GraphType{circle,triangle,rectangle}; class Graph{ public: virtual void draw(){} virtual ~Graph()=default; }; class Circle : public Graph{ public: void draw(); }; class Triangle: public Graph{ public: void draw(); }; class Rectangle: public Graph{ public: void draw(); }; class Canvas{ public: void add(const std::string& type); void paint() const; ~Canvas(); private: std::vector<Graph*>graphs; }; GraphType str_to_GraphType(const std::string& s); Graph* make_graph(const std::string& type);
demo3.cpp:
#include<string> #include"Graph.hpp" void test(){ Canvas canvas; canvas.add("circle"); canvas.add("triangle"); canvas.add("rectangle"); canvas.paint(); } int main(){ test(); }
result:
Q1:
1.
std::vector<Graph*>graphs;
用于存储Graph对象指针
2.
class Circle : public Graph{
public:
void draw();
};
class Triangle: public Graph{
public:
void draw();
};
class Rectangle: public Graph{
public:
void draw();
};
问题2：
1.若不使用虚函数则每次调用draw()都会调用Graph基类中draw()的方法
2.无法使用Graph中子类的属性
3.若不是虚函数则子类的析构函数不会被调用。
问题3：
enum class GraphType{circle,triangle,rectangle,star};
声明Star类：
class Star:public Graph{
public:
void draw();
}
实现Star::draw()
void star::draw(){std<<cout"draw a star...\n"}
str_to_GraphType:
if(t=="Star")return GraphType::star
再增加一个case:
case GraphType::star: return new star
问题4：
1.在析构函数中被释放
2.重复使用同一指针会导致无法确定哪个指针指向不明
任务四：
#ifndef TOY_HPP #define TOY_HPP #include <string> #include <memory> #include <vector> class Toy { public: virtual ~Toy() = default; virtual void show() const = 0; virtual void action() const = 0; }; class ElectronicToy : public Toy { public: ElectronicToy(const std::string& name); void show() const override; void action() const override; private: std::string name; }; class StuffedToy : public Toy { public: StuffedToy(const std::string& name); void show() const override; void action() const override; private: std::string name; }; class ToyFactory { public: void add(std::unique_ptr<Toy> toy); void display() const; private: std::vector<std::unique_ptr<Toy>> toys; };
toy.cpp
#include "toy.hpp" #include <iostream> #include <memory> int main() { ToyFactory factory; factory.add(std::make_unique<ElectronicToy>("音乐熊")); factory.add(std::make_unique<StuffedToy>("泰迪熊")); factory.add(std::make_unique<ElectronicToy>("机器人")); factory.display(); return 0; }
demo4:
#include <iostream> #include <memory> #include<toy.hpp> int main() { ToyFactory factory; factory.add(std::unique_ptr<Toy>(new ElectronicToy("音乐熊"))); factory.add(std::unique_ptr<Toy>(new StuffedToy("泰迪熊"))); factory.add(std::unique_ptr<Toy>(new ElectronicToy("机器人"))); factory.display(); return 0; }
result：
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