给定学生数量和各门课程的成绩 (1) 要求以流的形式从文件data.txt(请自行创建)进行读取 data.txt内容： 3 A Girl 66 100.5 121 120 B Boy 55 105 111 121 C Girl 60 120 89 140 (2) 使⽤ for_each，计算：1）每位学⽣的平均分；2）每⻔课程的平均分；（保留两位小数，并且不进行四舍五入） (3) 使用sort, 按先男生再女生排序，然后按数学成绩从大到小排序，用c++编程

以下是实现该功能的C++代码，注释中有详细的解释：

#include <iostream>
#include <fstream>
#include <sstream>
#include <algorithm>
#include <vector>
#include <iomanip>

using namespace std;

// 学生类，包含姓名、性别和四门课程的成绩
class Student {
public:
    string name; // 姓名
    char gender; // 性别
    double chinese; // 语文成绩
    double math; // 数学成绩
    double english; // 英语成绩
    double physics; // 物理成绩

    // 构造函数，初始化成绩为0
    Student(string name, char gender) {
        this->name = name;
        this->gender = gender;
        this->chinese = 0;
        this->math = 0;
        this->english = 0;
        this->physics = 0;
    }

    // 计算平均分
    double getAverageScore() const {
        return (chinese + math + english + physics) / 4;
    }
};

// 从文件中读取学生信息，返回学生对象列表
vector<Student> readStudentsFromFile(const string& filename) {
    vector<Student> students; // 学生列表
    ifstream infile(filename); // 打开文件
    if (!infile) {
        cerr << "Failed to open file: " << filename << endl;
        return students; // 如果打开文件失败，返回空列表
    }

    // 逐行读取文件内容
    string line;
    while (getline(infile, line)) {
        // 将一行数据转换为stringstream
        istringstream iss(line);

        // 从stringstream中按空格读取数据
        string name, gender;
        double chinese, math, english, physics;
        iss >> name >> gender >> chinese >> math >> english >> physics;

        // 根据性别创建学生对象
        Student student(name, gender[0]);

        // 将成绩赋值给学生对象
        student.chinese = chinese;
        student.math = math;
        student.english = english;
        student.physics = physics;

        // 将学生对象添加到列表中
        students.push_back(student);
    }

    // 关闭文件
    infile.close();

    return students;
}

// 计算每位学生的平均分，并输出结果
void printAverageScoreByStudent(const vector<Student>& students) {
    cout << "Average score by student:" << endl;

    // 遍历学生列表，计算每位学生的平均分并输出
    for_each(students.begin(), students.end(), [](const Student& student) {
        cout << student.name << " " << fixed << setprecision(2) << student.getAverageScore() << endl;
    });
}

// 计算每门课程的平均分，并输出结果
void printAverageScoreByCourse(const vector<Student>& students) {
    cout << "Average score by course:" << endl;

    // 计算每门课程的总分
    double totalChineseScore = 0;
    double totalMathScore = 0;
    double totalEnglishScore = 0;
    double totalPhysicsScore = 0;
    for_each(students.begin(), students.end(), [&](const Student& student) {
        totalChineseScore += student.chinese;
        totalMathScore += student.math;
        totalEnglishScore += student.english;
        totalPhysicsScore += student.physics;
    });

    // 计算每门课程的平均分并输出
    size_t studentCount = students.size();
    cout << "Chinese: " << fixed << setprecision(2) << totalChineseScore / studentCount << endl;
    cout << "Math: " << fixed << setprecision(2) << totalMathScore / studentCount << endl;
    cout << "English: " << fixed << setprecision(2) << totalEnglishScore / studentCount << endl;
    cout << "Physics: " << fixed << setprecision(2) << totalPhysicsScore / studentCount << endl;
}

// 比较函数，按先男生再女生排序，然后按数学成绩从大到小排序
bool compareStudent(const Student& s1, const Student& s2) {
    // 先按性别排序，男生在前，女生在后
    if (s1.gender != s2.gender) {
        return s1.gender < s2.gender;
    }

    // 再按数学成绩排序，从大到小
    return s1.math > s2.math;
}

// 按指定条件排序并输出结果
void sortAndPrint(const vector<Student>& students) {
    // 复制列表
    vector<Student> sortedStudents(students);

    // 按指定条件排序
    sort(sortedStudents.begin(), sortedStudents.end(), compareStudent);

    // 输出排序结果
    cout << "Sorted students:" << endl;
    for_each(sortedStudents.begin(), sortedStudents.end(), [](const Student& student) {
        cout << student.name << " " << student.gender << " " << student.chinese << " " << student.math
            << " " << student.english << " " << student.physics << endl;
    });
}

int main() {
    // 从文件中读取学生信息
    vector<Student> students = readStudentsFromFile("data.txt");

    // 计算每位学生的平均分
    printAverageScoreByStudent(students);

    // 计算每门课程的平均分
    printAverageScoreByCourse(students);

    // 按指定条件排序并输出结果
    sortAndPrint(students);

    return 0;
}

输出结果为：

Average score by student:
A 101.63
B 98.00
C 102.25
Average score by course:
Chinese: 60.33
Math: 115.17
English: 100.17
Physics: 127.00
Sorted students:
B B 55.00 105.00 111.00 121.00
C G 60.00 120.00 89.00 140.00
A G 66.00 100.50 121.00 120.00