用C++编写程序设计学生类Student和学生管理类StudentManger，并完成编码实现和测试，具体功能如下： （1）Student类包含学生学号、姓名、性别、分数等信息，定义构造函数、set函数、get函数等； （2）StudentManger类数据成员包含Student数组、学生个数，定义构造函数、save函数、read函数； （3）save函数的功能是将学生信息保存到文件中，read函数的功能是读取文件信息内容到Student数组中； （4）编写主函数完成功能测试。

以下是C++编写的程序：

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

const int MAX_STUDENT_NUM = 100;  // 学生数量上限

// 学生类
class Student {
public:
    // 构造函数
    Student(string id="", string name="", char gender=' ', float score=0.0) {
        this->id = id;
        this->name = name;
        this->gender = gender;
        this->score = score;
    }

    // set函数
    void setId(string id) {
        this->id = id;
    }

    void setName(string name) {
        this->name = name;
    }

    void setGender(char gender) {
        this->gender = gender;
    }

    void setScore(float score) {
        this->score = score;
    }

    // get函数
    string getId() const {
        return id;
    }

    string getName() const {
        return name;
    }

    char getGender() const {
        return gender;
    }

    float getScore() const {
        return score;
    }

private:
    string id;      // 学生学号
    string name;    // 学生姓名
    char gender;    // 学生性别
    float score;    // 学生分数
};

// 学生管理类
class StudentManager {
public:
    // 构造函数
    StudentManager() {
        studentNum = 0;
    }

    // 保存学生信息到文件中
    bool save(string filename) {
        ofstream fout(filename.c_str());
        if (!fout) {
            cout << "Error: cannot write to file " << filename << endl;
            return false;
        }
        fout << studentNum << endl;
        for (int i = 0; i < studentNum; i++) {
            fout << students[i].getId() << " "
                 << students[i].getName() << " "
                 << students[i].getGender() << " "
                 << students[i].getScore() << endl;
        }
        fout.close();
        return true;
    }

    // 从文件中读取学生信息
    bool read(string filename) {
        ifstream fin(filename.c_str());
        if (!fin) {
            cout << "Error: cannot open file " << filename << endl;
            return false;
        }
        fin >> studentNum;
        for (int i = 0; i < studentNum; i++) {
            string id, name;
            char gender;
            float score;
            fin >> id >> name >> gender >> score;
            students[i].setId(id);
            students[i].setName(name);
            students[i].setGender(gender);
            students[i].setScore(score);
        }
        fin.close();
        return true;
    }

    // 添加学生
    bool addStudent(Student student) {
        if (studentNum == MAX_STUDENT_NUM) {
            cout << "Error: too many students" << endl;
            return false;
        }
        students[studentNum++] = student;
        return true;
    }

    // 删除学生
    bool removeStudent(string id) {
        int index = -1;
        for (int i = 0; i < studentNum; i++) {
            if (students[i].getId() == id) {
                index = i;
                break;
            }
        }
        if (index == -1) {
            cout << "Error: student " << id << " not found" << endl;
            return false;
        }
        for (int i = index; i < studentNum - 1; i++) {
            students[i] = students[i+1];
        }
        studentNum--;
        return true;
    }

    // 修改学生信息
    bool modifyStudent(string id, Student student) {
        int index = -1;
        for (int i = 0; i < studentNum; i++) {
            if (students[i].getId() == id) {
                index = i;
                break;
            }
        }
        if (index == -1) {
            cout << "Error: student " << id << " not found" << endl;
            return false;
        }
        students[index] = student;
        return true;
    }

    // 根据学号查找学生
    Student* findStudentById(string id) {
        for (int i = 0; i < studentNum; i++) {
            if (students[i].getId() == id) {
                return &students[i];
            }
        }
        return NULL;
    }

    // 根据姓名查找学生
    Student* findStudentByName(string name) {
        for (int i = 0; i < studentNum; i++) {
            if (students[i].getName() == name) {
                return &students[i];
            }
        }
        return NULL;
    }

    // 显示所有学生信息
    void showAllStudents() {
        cout << "ID\tName\tGender\tScore" << endl;
        for (int i = 0; i < studentNum; i++) {
            cout << students[i].getId() << "\t"
                 << students[i].getName() << "\t"
                 << students[i].getGender() << "\t"
                 << students[i].getScore() << endl;
        }
    }

private:
    Student students[MAX_STUDENT_NUM];  // 学生数组
    int studentNum;                     // 学生数量
};

int main() {
    StudentManager manager;
    string filename = "students.txt";

    // 从文件中读取学生信息
    if (!manager.read(filename)) {
        return 1;
    }

    while (true) {
        cout << "1. Add Student" << endl;
        cout << "2. Remove Student" << endl;
        cout << "3. Modify Student" << endl;
        cout << "4. Find Student by ID" << endl;
        cout << "5. Find Student by Name" << endl;
        cout << "6. Show All Students" << endl;
        cout << "7. Save to File" << endl;
        cout << "0. Exit" << endl;
        cout << "Enter your choice: ";
        int choice;
        cin >> choice;

        switch (choice) {
        case 1: {
            string id, name;
            char gender;
            float score;
            cout << "Enter student ID: ";
            cin >> id;
            cout << "Enter student name: ";
            cin >> name;
            cout << "Enter student gender (M/F): ";
            cin >> gender;
            cout << "Enter student score: ";
            cin >> score;
            Student student(id, name, gender, score);
            manager.addStudent(student);
            break;
        }
        case 2: {
            string id;
            cout << "Enter student ID: ";
            cin >> id;
            manager.removeStudent(id);
            break;
        }
        case 3: {
            string id, name;
            char gender;
            float score;
            cout << "Enter student ID: ";
            cin >> id;
            Student* student = manager.findStudentById(id);
            if (student == NULL) {
                break;
            }
            cout << "Enter student name: ";
            cin >> name;
            cout << "Enter student gender (M/F): ";
            cin >> gender;
            cout << "Enter student score: ";
            cin >> score;
            student->setName(name);
            student->setGender(gender);
            student->setScore(score);
            manager.modifyStudent(id, *student);
            break;
        }
        case 4: {
            string id;
            cout << "Enter student ID: ";
            cin >> id;
            Student* student = manager.findStudentById(id);
            if (student == NULL) {
                cout << "Error: student " << id << " not found" << endl;
                break;
            }
            cout << "ID\tName\tGender\tScore" << endl;
            cout << student->getId() << "\t"
                 << student->getName() << "\t"
                 << student->getGender() << "\t"
                 << student->getScore() << endl;
            break;
        }
        case 5: {
            string name;
            cout << "Enter student name: ";
            cin >> name;
            Student* student = manager.findStudentByName(name);
            if (student == NULL) {
                cout << "Error: student " << name << " not found" << endl;
                break;
            }
            cout << "ID\tName\tGender\tScore" << endl;
            cout << student->getId() << "\t"
                 << student->getName() << "\t"
                 << student->getGender() << "\t"
                 << student->getScore() << endl;
            break;
        }
        case 6: {
            manager.showAllStudents();
            break;
        }
        case 7: {
            if (!manager.save(filename)) {
                return 1;
            }
            break;
        }
        case 0: {
            return 0;
        }
        default: {
            cout << "Invalid input" << endl;
            break;
        }
        }
    }
}

该程序实现了学生类和学生管理类，包括以下功能：

1. 添加学生
2. 删除学生
3. 修改学生信息
4. 根据学号查找学生
5. 根据姓名查找学生
6. 显示所有学生信息
7. 保存学生信息到文件中
8. 从文件中读取学生信息

在主函数中，我们通过一个死循环来实现不断的输入和处理用户的选择。根据用户的选择，调用相应的学生管理类中的函数来实现功能。用户可以选择在程序退出前将学生信息保存到文件中。