c++按课程统计每门课程的平均成绩、最高分和最低分；

这个问题需要使用数据库中的聚合函数来实现。假设我们有一个名为"score"的表，包含以下字段：

- course：课程名称
- student：学生姓名
- score：学生成绩

我们可以使用以下SQL语句来按课程统计每门课程的平均成绩、最高分和最低分：

SELECT course, AVG(score) AS avg_score, MAX(score) AS max_score, MIN(score) AS min_score
FROM score
GROUP BY course;

这个查询语句将score表按照课程名称进行分组，然后使用AVG、MAX和MIN聚合函数计算每门课程的平均成绩、最高分和最低分。最后，查询结果将按照课程名称进行排序返回。

相关问题

1. 定义学生类，包括学号、姓名、性别、多门课程的成绩；假设有n个学生，由键盘输入学生信息； 2.定义类成员函数，计算每个学生的平均成绩； 3.按课程统计每门课程的平均成绩、最高分和最低分； 4.同时输出所有学生信息； 5. 通过输入学生学号或姓名查询某学生的信息。

1. 定义学生类：

class Student {
private:
    string id; // 学号
    string name; // 姓名
    string gender; // 性别
    vector<double> scores; // 多门课程的成绩
public:
    Student(string id, string name, string gender, vector<double> scores) {
        this->id = id;
        this->name = name;
        this->gender = gender;
        this->scores = scores;
    }
    double getAverageScore() { // 计算平均成绩
        double sum = 0;
        for (double score : scores) {
            sum += score;
        }
        return sum / scores.size();
    }
    string getId() { // 获取学号
        return id;
    }
    string getName() { // 获取姓名
        return name;
    }
    string getGender() { // 获取性别
        return gender;
    }
    vector<double> getScores() { // 获取成绩
        return scores;
    }
};

2. 输入学生信息：

vector<Student> students;
int n;
cout << "请输入学生人数：";
cin >> n;
for (int i = 0; i < n; i++) {
    string id, name, gender;
    vector<double> scores;
    cout << "请输入第" << i + 1 << "个学生的学号、姓名、性别和多门课程的成绩：";
    cin >> id >> name >> gender;
    for (int j = 0; j < 3; j++) {
        double score;
        cin >> score;
        scores.push_back(score);
    }
    Student student(id, name, gender, scores);
    students.push_back(student);
}

3. 统计每门课程的平均成绩、最高分和最低分：

vector<double> chineseScores, mathScores, englishScores;
for (Student student : students) {
    chineseScores.push_back(student.getScores()[0]);
    mathScores.push_back(student.getScores()[1]);
    englishScores.push_back(student.getScores()[2]);
}
double chineseAverage = accumulate(chineseScores.begin(), chineseScores.end(), 0.0) / chineseScores.size();
double mathAverage = accumulate(mathScores.begin(), mathScores.end(), 0.0) / mathScores.size();
double englishAverage = accumulate(englishScores.begin(), englishScores.end(), 0.0) / englishScores.size();
double chineseMax = *max_element(chineseScores.begin(), chineseScores.end());
double mathMax = *max_element(mathScores.begin(), mathScores.end());
double englishMax = *max_element(englishScores.begin(), englishScores.end());
double chineseMin = *min_element(chineseScores.begin(), chineseScores.end());
double mathMin = *min_element(mathScores.begin(), mathScores.end());
double englishMin = *min_element(englishScores.begin(), englishScores.end());
cout << "语文平均成绩：" << chineseAverage << "，最高分：" << chineseMax << "，最低分：" << chineseMin << endl;
cout << "数学平均成绩：" << mathAverage << "，最高分：" << mathMax << "，最低分：" << mathMin << endl;
cout << "英语平均成绩：" << englishAverage << "，最高分：" << englishMax << "，最低分：" << englishMin << endl;

4. 输出所有学生信息：

cout << "所有学生信息：" << endl;
for (Student student : students) {
    cout << "学号：" << student.getId() << "，姓名：" << student.getName() << "，性别：" << student.getGender() << "，成绩：";
    for (double score : student.getScores()) {
        cout << score << " ";
    }
    cout << "，平均成绩：" << student.getAverageScore() << endl;
}

5. 查询某学生的信息：

string query;
cout << "请输入查询学生的学号或姓名：";
cin >> query;
for (Student student : students) {
    if (query == student.getId() || query == student.getName()) {
        cout << "学号：" << student.getId() << "，姓名：" << student.getName() << "，性别：" << student.getGender() << "，成绩：";
        for (double score : student.getScores()) {
            cout << score << " ";
        }
        cout << "，平均成绩：" << student.getAverageScore() << endl;
    }
}

问题描述:设学生信息包括:学号、姓名、期末成绩、平时成绩，对学生的学习成绩信息进行管理。 设计要求: 实现学生信息的录入、修改、插入、删除、查询、计算总评成绩、根据总评程序排序和划分等级、按学号查询学生成绩等。 (1)从文件输入学生的成绩信息，包含学号、姓名、期末成绩和平时成绩; (2)显示全部学生成绩信息; (3)更新某个学生的基本信息或课程成绩; (4)对成绩统计分析(总分、平均分、最高分、最低分、及格率等);(5)学号查找并显示某个学生的成绩;(6)按姓名查找并显示某个学生的成绩;(7)按总评成绩由高到低排序显示;(8)统计各分数段人数并显示; (9)设计一个菜单，具有上述规定的操作要求、退出系统等最基本的功能。（全部功能在devc++中一个程序实现）

这是一个典型的学生信息管理系统，可以使用C++语言实现。下面是一个简单的实现示例：

#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
using namespace std;

struct Student {
    string id;
    string name;
    double final_score;
    double regular_score;
    double total_score;
    char level;
};

vector<Student> students;

void load_data(string filename) {
    ifstream fin(filename);
    if (!fin.is_open()) {
        cout << "Failed to open file " << filename << endl;
        return;
    }
    students.clear();
    while (!fin.eof()) {
        Student s;
        fin >> s.id >> s.name >> s.final_score >> s.regular_score;
        s.total_score = s.final_score * 0.6 + s.regular_score * 0.4;
        students.push_back(s);
    }
    fin.close();
}

void save_data(string filename) {
    ofstream fout(filename);
    if (!fout.is_open()) {
        cout << "Failed to open file " << filename << endl;
        return;
    }
    for (int i = 0; i < students.size(); i++) {
        Student s = students[i];
        fout << s.id << " " << s.name << " " << s.final_score << " " << s.regular_score << endl;
    }
    fout.close();
}

void display_all() {
    cout << "ID\tName\tFinal\tRegular\tTotal\tLevel" << endl;
    for (int i = 0; i < students.size(); i++) {
        Student s = students[i];
        cout << s.id << "\t" << s.name << "\t" << s.final_score << "\t" << s.regular_score << "\t"
             << s.total_score << "\t" << s.level << endl;
    }
}

void update_student() {
    string id;
    cout << "Enter the student ID to update: ";
    cin >> id;
    for (int i = 0; i < students.size(); i++) {
        if (students[i].id == id) {
            cout << "Enter new name: ";
            cin >> students[i].name;
            cout << "Enter new final score: ";
            cin >> students[i].final_score;
            cout << "Enter new regular score: ";
            cin >> students[i].regular_score;
            students[i].total_score = students[i].final_score * 0.6 + students[i].regular_score * 0.4;
            return;
        }
    }
    cout << "No such student found." << endl;
}

void calculate_statistics() {
    double total = 0, average = 0, max_score = 0, min_score = 100;
    int pass_count = 0, fail_count = 0;
    for (int i = 0; i < students.size(); i++) {
        Student s = students[i];
        total += s.total_score;
        if (s.total_score >= 60) {
            pass_count++;
        } else {
            fail_count++;
        }
        if (s.total_score > max_score) {
            max_score = s.total_score;
        }
        if (s.total_score < min_score) {
            min_score = s.total_score;
        }
    }
    average = total / students.size();
    cout << "Total: " << total << endl;
    cout << "Average: " << average << endl;
    cout << "Highest score: " << max_score << endl;
    cout << "Lowest score: " << min_score << endl;
    cout << "Pass count: " << pass_count << endl;
    cout << "Fail count: " << fail_count << endl;
}

void find_by_id() {
    string id;
    cout << "Enter the student ID to search: ";
    cin >> id;
    for (int i = 0; i < students.size(); i++) {
        if (students[i].id == id) {
            Student s = students[i];
            cout << "ID\tName\tFinal\tRegular\tTotal\tLevel" << endl;
            cout << s.id << "\t" << s.name << "\t" << s.final_score << "\t" << s.regular_score << "\t"
                 << s.total_score << "\t" << s.level << endl;
            return;
        }
    }
    cout << "No such student found." << endl;
}

void find_by_name() {
    string name;
    cout << "Enter the student name to search: ";
    cin >> name;
    for (int i = 0; i < students.size(); i++) {
        if (students[i].name == name) {
            Student s = students[i];
            cout << "ID\tName\tFinal\tRegular\tTotal\tLevel" << endl;
            cout << s.id << "\t" << s.name << "\t" << s.final_score << "\t" << s.regular_score << "\t"
                 << s.total_score << "\t" << s.level << endl;
        }
    }
}

void sort_by_total_score() {
    sort(students.begin(), students.end(), [](const Student &a, const Student &b) {
        return a.total_score > b.total_score;
    });
    display_all();
}

void count_level() {
    int level_A = 0, level_B = 0, level_C = 0, level_D = 0, level_E = 0;
    for (int i = 0; i < students.size(); i++) {
        if (students[i].total_score >= 90) {
            level_A++;
            students[i].level = 'A';
        } else if (students[i].total_score >= 80) {
            level_B++;
            students[i].level = 'B';
        } else if (students[i].total_score >= 70) {
            level_C++;
            students[i].level = 'C';
        } else if (students[i].total_score >= 60) {
            level_D++;
            students[i].level = 'D';
        } else {
            level_E++;
            students[i].level = 'E';
        }
    }
    cout << "A: " << level_A << endl;
    cout << "B: " << level_B << endl;
    cout << "C: " << level_C << endl;
    cout << "D: " << level_D << endl;
    cout << "E: " << level_E << endl;
}

void menu() {
    while (true) {
        cout << "1. Load data" << endl;
        cout << "2. Save data" << endl;
        cout << "3. Display all data" << endl;
        cout << "4. Update student information" << endl;
        cout << "5. Calculate statistics" << endl;
        cout << "6. Find student by ID" << endl;
        cout << "7. Find student by name" << endl;
        cout << "8. Sort by total score" << endl;
        cout << "9. Count level" << endl;
        cout << "0. Exit" << endl;
        int option;
        cin >> option;
        switch (option) {
            case 1:
                load_data("students.txt");
                break;
            case 2:
                save_data("students.txt");
                break;
            case 3:
                display_all();
                break;
            case 4:
                update_student();
                break;
            case 5:
                calculate_statistics();
                break;
            case 6:
                find_by_id();
                break;
            case 7:
                find_by_name();
                break;
            case 8:
                sort_by_total_score();
                break;
            case 9:
                count_level();
                break;
            case 0:
                return;
            default:
                cout << "Invalid option." << endl;
        }
    }
}

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

注意，这只是一个简单的实现示例，实际应用中可能需要更多的功能和更完善的错误处理。