是纯文本文件，每行记录分别包括学号、姓名和成绩，文件名字：student.txt，文件路径：C:\STL

好的，我已经了解了文件的格式和路径。接下来，我将分别实现你的三个功能：

1.依据学生学号查询并输出对应学生的姓名及成绩：

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

struct Student {
    int id;
    string name;
    double score;
};

bool cmp(const Student& a, const Student& b) {
    return a.score < b.score;
}

int main() {
    vector<Student> students;
    ifstream fin("C:\\STL\\student.txt");
    int id;
    string name;
    double score;
    while (fin >> id >> name >> score) {
        students.push_back({ id, name, score });
    }

    // 依据学生学号查询并输出对应学生的姓名及成绩
    int queryId;
    cout << "请输入要查询的学生学号：";
    cin >> queryId;
    for (const auto& s : students) {
        if (s.id == queryId) {
            cout << "姓名：" << s.name << "，成绩：" << s.score << endl;
            break;
        }
    }

    // 按照学生成绩升序排列并输出结果
    sort(students.begin(), students.end(), cmp);
    cout << "按照成绩升序排列的结果：" << endl;
    for (const auto& s : students) {
        cout << "学号：" << s.id << "，姓名：" << s.name << "，成绩：" << s.score << endl;
    }

    // 查询并输出平均成绩最高的前五名同学的学号，成绩及平均成绩
    sort(students.rbegin(), students.rend(), cmp);
    cout << "平均成绩最高的前五名同学的结果：" << endl;
    double sum = 0;
    int count = 0;
    for (int i = 0; i < min(5, (int)students.size()); i++) {
        cout << "学号：" << students[i].id << "，姓名：" << students[i].name << "，成绩：" << students[i].score << endl;
        sum += students[i].score;
        count++;
    }
    cout << "平均成绩：" << sum / count << endl;

    return 0;
}

2.按照学生成绩升序排列并输出结果：

bool cmp(const Student& a, const Student& b) {
    return a.score < b.score;
}

int main() {
    vector<Student> students;
    ifstream fin("C:\\STL\\student.txt");
    int id;
    string name;
    double score;
    while (fin >> id >> name >> score) {
        students.push_back({ id, name, score });
    }

    // 依据学生学号查询并输出对应学生的姓名及成绩
    int queryId;
    cout << "请输入要查询的学生学号：";
    cin >> queryId;
    for (const auto& s : students) {
        if (s.id == queryId) {
            cout << "姓名：" << s.name << "，成绩：" << s.score << endl;
            break;
        }
    }

    // 按照学生成绩升序排列并输出结果
    sort(students.begin(), students.end(), cmp);
    cout << "按照成绩升序排列的结果：" << endl;
    for (const auto& s : students) {
        cout << "学号：" << s.id << "，姓名：" << s.name << "，成绩：" << s.score << endl;
    }

    // 查询并输出平均成绩最高的前五名同学的学号，成绩及平均成绩
    sort(students.rbegin(), students.rend(), cmp);
    cout << "平均成绩最高的前五名同学的结果：" << endl;
    double sum = 0;
    int count = 0;
    for (int i = 0; i < min(5, (int)students.size()); i++) {
        cout << "学号：" << students[i].id << "，姓名：" << students[i].name << "，成绩：" << students[i].score << endl;
        sum += students[i].score;
        count++;
    }
    cout << "平均成绩：" << sum / count << endl;

    return 0;
}

3.查询并输出平均成绩最高的前五名同学的学号，成绩及平均成绩：

bool cmp(const Student& a, const Student& b) {
    return a.score < b.score;
}

int main() {
    vector<Student> students;
    ifstream fin("C:\\STL\\student.txt");
    int id;
    string name;
    double score;
    while (fin >> id >> name >> score) {
        students.push_back({ id, name, score });
    }

    // 依据学生学号查询并输出对应学生的姓名及成绩
    int queryId;
    cout << "请输入要查询的学生学号：";
    cin >> queryId;
    for (const auto& s : students) {
        if (s.id == queryId) {
            cout << "姓名：" << s.name << "，成绩：" << s.score << endl;
            break;
        }
    }

    // 按照学生成绩升序排列并输出结果
    sort(students.begin(), students.end(), cmp);
    cout << "按照成绩升序排列的结果：" << endl;
    for (const auto& s : students) {
        cout << "学号：" << s.id << "，姓名：" << s.name << "，成绩：" << s.score << endl;
    }

    // 查询并输出平均成绩最高的前五名同学的学号，成绩及平均成绩
    sort(students.rbegin(), students.rend(), cmp);
    cout << "平均成绩最高的前五名同学的结果：" << endl;
    double sum = 0;
    int count = 0;
    for (int i = 0; i < min(5, (int)students.size()); i++) {
        cout << "学号：" << students[i].id << "，姓名：" << students[i].name << "，成绩：" << students[i].score << endl;
        sum += students[i].score;
        count++;
    }
    cout << "平均成绩：" << sum / count << endl;

    return 0;
}

希望这些代码能满足你的需求。