定义一个结构体数组存放十个学生的学号，姓名和成绩，从键盘输入这十个学生的以上内容，存入文件stud.txt，关闭文件，打开文件，将数据读出，查看是否正确再关闭文件，打开文件，读出数据，将十个学生按照平均分进行由高到低的排序，分别将结果输出到屏幕上和另一个文件studsort.txt中

以下是代码实现：

#include <iostream>
#include <fstream>
#include <algorithm>

using namespace std;

const int MAX_STUDENTS = 10;

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

bool compare(const Student& s1, const Student& s2) {
    return s1.score > s2.score;
}

int main() {
    Student students[MAX_STUDENTS];

    // 从键盘输入学生信息
    for (int i = 0; i < MAX_STUDENTS; i++) {
        cout << "请输入第" << i+1 << "个学生的学号、姓名和成绩：";
        cin >> students[i].id >> students[i].name >> students[i].score;
    }

    // 存入文件stud.txt
    ofstream ofs("stud.txt");
    if (!ofs) {
        cerr << "无法打开文件" << endl;
        return 1;
    }

    for (int i = 0; i < MAX_STUDENTS; i++) {
        ofs << students[i].id << " " << students[i].name << " " << students[i].score << endl;
    }
    ofs.close();

    // 读取文件stud.txt中的数据
    ifstream ifs("stud.txt");
    if (!ifs) {
        cerr << "无法打开文件" << endl;
        return 1;
    }

    for (int i = 0; i < MAX_STUDENTS; i++) {
        ifs >> students[i].id >> students[i].name >> students[i].score;
    }
    ifs.close();

    // 按照平均分排序
    sort(students, students + MAX_STUDENTS, compare);

    // 输出到屏幕和文件studsort.txt中
    ofstream ofs_sort("studsort.txt");
    if (!ofs_sort) {
        cerr << "无法打开文件" << endl;
        return 1;
    }

    cout << "排序后的结果：" << endl;
    ofs_sort << "排序后的结果：" << endl;

    for (int i = 0; i < MAX_STUDENTS; i++) {
        cout << students[i].id << " " << students[i].name << " " << students[i].score << endl;
        ofs_sort << students[i].id << " " << students[i].name << " " << students[i].score << endl;
    }

    ofs_sort.close();

    return 0;
}