用c语言写一个学生学籍管理系统 主要功能: 欢迎及菜单页面 通过文本文件读入学生信息 新增学生(学号不可重复) 录入成绩 删除学生 展示所有学生信息 计算最高最低平均成绩 统计ABCD每个分段的人数 按成绩从高到低排序 按学号排序 退出前将所有学生信息回写进文本文档

这是一个比较全面的学生学籍管理系统，需要一定的编程基础才能完成。下面是一个简单的参考代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_STUDENT_NUM 1000

typedef struct {
    char id[20];
    char name[20];
    int score;
} Student;

Student students[MAX_STUDENT_NUM];
int student_num = 0;

void read_students_from_file() {
    FILE *fp = fopen("students.txt", "r");
    if (fp == NULL) {
        printf("无法打开文件！\n");
        return;
    }
    char line[100];
    while (fgets(line, 100, fp) != NULL) {
        sscanf(line, "%s %s %d", students[student_num].id, students[student_num].name, &students[student_num].score);
        student_num++;
    }
    fclose(fp);
}

void save_students_to_file() {
    FILE *fp = fopen("students.txt", "w");
    if (fp == NULL) {
        printf("无法打开文件！\n");
        return;
    }
    for (int i = 0; i < student_num; i++) {
        fprintf(fp, "%s %s %d\n", students[i].id, students[i].name, students[i].score);
    }
    fclose(fp);
}

void add_student() {
    if (student_num >= MAX_STUDENT_NUM) {
        printf("学生人数已达上限！\n");
        return;
    }
    Student new_student;
    printf("请输入学生学号：");
    scanf("%s", new_student.id);
    for (int i = 0; i < student_num; i++) {
        if (strcmp(students[i].id, new_student.id) == 0) {
            printf("学号已存在！\n");
            return;
        }
    }
    printf("请输入学生姓名：");
    scanf("%s", new_student.name);
    printf("请输入学生成绩：");
    scanf("%d", &new_student.score);
    students[student_num++] = new_student;
    printf("添加成功！\n");
}

void delete_student() {
    char id[20];
    printf("请输入要删除的学生学号：");
    scanf("%s", id);
    for (int i = 0; i < student_num; i++) {
        if (strcmp(students[i].id, id) == 0) {
            for (int j = i; j < student_num - 1; j++) {
                students[j] = students[j + 1];
            }
            student_num--;
            printf("删除成功！\n");
            return;
        }
    }
    printf("学号不存在！\n");
}

void show_all_students() {
    printf("学号\t姓名\t成绩\n");
    for (int i = 0; i < student_num; i++) {
        printf("%s\t%s\t%d\n", students[i].id, students[i].name, students[i].score);
    }
}

void sort_by_score() {
    for (int i = 0; i < student_num - 1; i++) {
        for (int j = 0; j < student_num - i - 1; j++) {
            if (students[j].score < students[j + 1].score) {
                Student temp = students[j];
                students[j] = students[j + 1];
                students[j + 1] = temp;
            }
        }
    }
    printf("排序成功！\n");
}

void sort_by_id() {
    for (int i = 0; i < student_num - 1; i++) {
        for (int j = 0; j < student_num - i - 1; j++) {
            if (strcmp(students[j].id, students[j + 1].id) > 0) {
                Student temp = students[j];
                students[j] = students[j + 1];
                students[j + 1] = temp;
            }
        }
    }
    printf("排序成功！\n");
}

void calculate_scores() {
    int max_score = 0, min_score = 100, sum_score = 0;
    int count_a = 0, count_b = 0, count_c = 0, count_d = 0;
    for (int i = 0; i < student_num; i++) {
        max_score = students[i].score > max_score ? students[i].score : max_score;
        min_score = students[i].score < min_score ? students[i].score : min_score;
        sum_score += students[i].score;
        if (students[i].score >= 90) {
            count_a++;
        } else if (students[i].score >= 80) {
            count_b++;
        } else if (students[i].score >= 70) {
            count_c++;
        } else {
            count_d++;
        }
    }
    printf("最高分：%d\n", max_score);
    printf("最低分：%d\n", min_score);
    printf("平均分：%.2f\n", (float)sum_score / student_num);
    printf("A段人数：%d\n", count_a);
    printf("B段人数：%d\n", count_b);
    printf("C段人数：%d\n", count_c);
    printf("D段人数：%d\n", count_d);
}

int main() {
    read_students_from_file();
    while (1) {
        printf("\n");
        printf("学生学籍管理系统\n");
        printf("1. 新增学生\n");
        printf("2. 录入成绩\n");
        printf("3. 删除学生\n");
        printf("4. 展示所有学生信息\n");
        printf("5. 计算最高最低平均成绩\n");
        printf("6. 统计ABCD每个分段的人数\n");
        printf("7. 按成绩从高到低排序\n");
        printf("8. 按学号排序\n");
        printf("9. 退出并保存\n");
        printf("请选择操作：");
        int choice;
        scanf("%d", &choice);
        switch (choice) {
            case 1:
                add_student();
                break;
            case 2:
                printf("请输入要录入成绩的学生学号：");
                char id[20];
                scanf("%s", id);
                for (int i = 0; i < student_num; i++) {
                    if (strcmp(students[i].id, id) == 0) {
                        printf("请输入成绩：");
                        scanf("%d", &students[i].score);
                        printf("成绩录入成功！\n");
                        break;
                    }
                    if (i == student_num - 1) {
                        printf("学号不存在！\n");
                    }
                }
                break;
            case 3:
                delete_student();
                break;
            case 4:
                show_all_students();
                break;
            case 5:
                calculate_scores();
                break;
            case 6:
                calculate_scores();
                break;
            case 7:
                sort_by_score();
                break;
            case 8:
                sort_by_id();
                break;
            case 9:
                save_students_to_file();
                printf("已保存并退出！\n");
                return 0;
            default:
                printf("无效的操作！\n");
                break;
        }
    }
}

需要注意的是，上述代码中使用了一个结构体 `Student` 来存储学生信息，其中包括学号、姓名和成绩。同时，我们将所有的学生信息存储在一个全局数组 `students` 中，最大长度为 `MAX_STUDENT_NUM`。在主函数中，我们通过 `read_students_from_file` 函数从文件中读取学生信息，并通过 `save_students_to_file` 函数将所有学生信息写回文件。对于其他的功能，我们分别定义了相应的函数来实现。