（1）用标准C语言实现一个字符版的仅用于本班级的系统； （2）支持学生基本信息的管理，包括增加、删除、修改、查找学生； （3）支持课程基本信息的管理，包括增加、删除、修改、查找课程； （4）至少支持高等数学、程序设计基础、线性代数等三门课程的成绩管理； （5）支持学生、课程、成绩等信息的文件存储、文件加载，与显示； （6）支持管理员与普通用户两种角色，普通用户只能查看信息，管理员可以修改信息； （7）界面友好，使用方便。

好的，那么这个系统需要实现的功能比较复杂，需要设计良好的数据结构和算法。下面是一个简单的示例代码，提供给您参考：

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

#define MAX_STUDENT_NUM 100
#define MAX_COURSE_NUM 3
#define MAX_NAME_LENGTH 20

typedef struct {
    char name[MAX_NAME_LENGTH];
    int id;
    int age;
    char sex;
} student;

typedef struct {
    char name[MAX_NAME_LENGTH];
    int id;
} course;

typedef struct {
    int student_id;
    int course_id;
    int score;
} grade;

student students[MAX_STUDENT_NUM];
course courses[MAX_COURSE_NUM];
grade grades[MAX_STUDENT_NUM * MAX_COURSE_NUM];
int student_num = 0;
int course_num = 0;
int grade_num = 0;

void add_student() {
    if (student_num >= MAX_STUDENT_NUM) {
        printf("Too many students!\n");
        return;
    }
    printf("Enter student name: ");
    scanf("%s", students[student_num].name);
    printf("Enter student id: ");
    scanf("%d", &students[student_num].id);
    printf("Enter student age: ");
    scanf("%d", &students[student_num].age);
    printf("Enter student sex: ");
    scanf(" %c", &students[student_num].sex);
    student_num++;
}

void delete_student() {
    int id_to_delete;
    printf("Enter student id to delete: ");
    scanf("%d", &id_to_delete);
    int i;
    for (i = 0; i < student_num; i++) {
        if (students[i].id == id_to_delete) {
            int j;
            for (j = i; j < student_num - 1; j++) {
                students[j] = students[j + 1];
            }
            student_num--;
            printf("Delete student success!\n");
            return;
        }
    }
    printf("Student not found!\n");
}

void modify_student() {
    int id_to_modify;
    printf("Enter student id to modify: ");
    scanf("%d", &id_to_modify);
    int i;
    for (i = 0; i < student_num; i++) {
        if (students[i].id == id_to_modify) {
            printf("Enter new student name: ");
            scanf("%s", students[i].name);
            printf("Enter new student age: ");
            scanf("%d", &students[i].age);
            printf("Enter new student sex: ");
            scanf(" %c", &students[i].sex);
            printf("Modify student success!\n");
            return;
        }
    }
    printf("Student not found!\n");
}

void search_student() {
    int id_to_search;
    printf("Enter student id to search: ");
    scanf("%d", &id_to_search);
    int i;
    for (i = 0; i < student_num; i++) {
        if (students[i].id == id_to_search) {
            printf("Student name: %s\n", students[i].name);
            printf("Student id: %d\n", students[i].id);
            printf("Student age: %d\n", students[i].age);
            printf("Student sex: %c\n", students[i].sex);
            return;
        }
    }
    printf("Student not found!\n");
}

void add_course() {
    if (course_num >= MAX_COURSE_NUM) {
        printf("Too many courses!\n");
        return;
    }
    printf("Enter course name: ");
    scanf("%s", courses[course_num].name);
    printf("Enter course id: ");
    scanf("%d", &courses[course_num].id);
    course_num++;
}

void delete_course() {
    int id_to_delete;
    printf("Enter course id to delete: ");
    scanf("%d", &id_to_delete);
    int i;
    for (i = 0; i < course_num; i++) {
        if (courses[i].id == id_to_delete) {
            int j;
            for (j = i; j < course_num - 1; j++) {
                courses[j] = courses[j + 1];
            }
            course_num--;
            printf("Delete course success!\n");
            return;
        }
    }
    printf("Course not found!\n");
}

void modify_course() {
    int id_to_modify;
    printf("Enter course id to modify: ");
    scanf("%d", &id_to_modify);
    int i;
    for (i = 0; i < course_num; i++) {
        if (courses[i].id == id_to_modify) {
            printf("Enter new course name: ");
            scanf("%s", courses[i].name);
            printf("Modify course success!\n");
            return;
        }
    }
    printf("Course not found!\n");
}

void search_course() {
    int id_to_search;
    printf("Enter course id to search: ");
    scanf("%d", &id_to_search);
    int i;
    for (i = 0; i < course_num; i++) {
        if (courses[i].id == id_to_search) {
            printf("Course name: %s\n", courses[i].name);
            printf("Course id: %d\n", courses[i].id);
            return;
        }
    }
    printf("Course not found!\n");
}

void add_grade() {
    if (grade_num >= MAX_STUDENT_NUM * MAX_COURSE_NUM) {
        printf("Too many grades!\n");
        return;
    }
    int student_id, course_id, score;
    printf("Enter student id: ");
    scanf("%d", &student_id);
    printf("Enter course id: ");
    scanf("%d", &course_id);
    printf("Enter score: ");
    scanf("%d", &score);
    grades[grade_num].student_id = student_id;
    grades[grade_num].course_id = course_id;
    grades[grade_num].score = score;
    grade_num++;
}

void delete_grade() {
    int student_id_to_delete, course_id_to_delete;
    printf("Enter student id to delete: ");
    scanf("%d", &student_id_to_delete);
    printf("Enter course id to delete: ");
    scanf("%d", &course_id_to_delete);
    int i;
    for (i = 0; i < grade_num; i++) {
        if (grades[i].student_id == student_id_to_delete && grades[i].course_id == course_id_to_delete) {
            int j;
            for (j = i; j < grade_num - 1; j++) {
                grades[j] = grades[j + 1];
            }
            grade_num--;
            printf("Delete grade success!\n");
            return;
        }
    }
    printf("Grade not found!\n");
}

void modify_grade() {
    int student_id_to_modify, course_id_to_modify;
    printf("Enter student id to modify: ");
    scanf("%d", &student_id_to_modify);
    printf("Enter course id to modify: ");
    scanf("%d", &course_id_to_modify);
    int i;
    for (i = 0; i < grade_num; i++) {
        if (grades[i].student_id == student_id_to_modify && grades[i].course_id == course_id_to_modify) {
            printf("Enter new score: ");
            scanf("%d", &grades[i].score);
            printf("Modify grade success!\n");
            return;
        }
    }
    printf("Grade not found!\n");
}

void search_grade() {
    int student_id_to_search, course_id_to_search;
    printf("Enter student id to search: ");
    scanf("%d", &student_id_to_search);
    printf("Enter course id to search: ");
    scanf("%d", &course_id_to_search);
    int i;
    for (i = 0; i < grade_num; i++) {
        if (grades[i].student_id == student_id_to_search && grades[i].course_id == course_id_to_search) {
            printf("Student id: %d\n", grades[i].student_id);
            printf("Course id: %d\n", grades[i].course_id);
            printf("Score: %d\n", grades[i].score);
            return;
        }
    }
    printf("Grade not found!\n");
}

void save_data() {
    FILE *fp = fopen("data.txt", "w");
    if (fp == NULL) {
        printf("Cannot open file!\n");
        return;
    }
    fprintf(fp, "%d %d %d\n", student_num, course_num, grade_num);
    int i;
    for (i = 0; i < student_num; i++) {
        fprintf(fp, "%s %d %d %c\n", students[i].name, students[i].id, students[i].age, students[i].sex);
    }
    for (i = 0; i < course_num; i++) {
        fprintf(fp, "%s %d\n", courses[i].name, courses[i].id);
    }
    for (i = 0; i < grade_num; i++) {
        fprintf(fp, "%d %d %d\n", grades[i].student_id, grades[i].course_id, grades[i].score);
    }
    fclose(fp);
    printf("Save data success!\n");
}

void load_data() {
    FILE *fp = fopen("data.txt", "r");
    if (fp == NULL) {
        printf("Cannot open file!\n");
        return;
    }
    fscanf(fp, "%d %d %d\n", &student_num, &course_num, &grade_num);
    int i;
    for (i = 0; i < student_num; i++) {
        fscanf(fp, "%s %d %d %c\n", students[i].name, &students[i].id, &students[i].age, &students[i].sex);
    }
    for (i = 0; i < course_num; i++) {
        fscanf(fp, "%s %d\n", courses[i].name, &courses[i].id);
    }
    for (i = 0; i < grade_num; i++) {
        fscanf(fp, "%d %d %d\n", &grades[i].student_id, &grades[i].course_id, &grades[i].score);
    }
    fclose(fp);
    printf("Load data success!\n");
}

void display_students() {
    printf("Student List:\n");
    int i;
    for (i = 0; i < student_num; i++) {
        printf("Student name: %s\n", students[i].name);
        printf("Student id: %d\n", students[i].id);
        printf("Student age: %d\n", students[i].age);
        printf("Student sex: %c\n", students[i].sex);
        printf("\n");
    }
}

void display_courses() {
    printf("Course List:\n");
    int i;
    for (i = 0; i < course_num; i++) {
        printf("Course name: %s\n", courses[i].name);
        printf("Course id: %d\n", courses[i].id);
        printf("\n");
    }
}

void display_grades() {
    printf("Grade List:\n");
    int i;
    for (i = 0; i < grade_num; i++) {
        printf("Student id: %d\n", grades[i].student_id);
        printf("Course id: %d\n", grades[i].course_id);
        printf("Score: %d\n", grades[i].score);
        printf("\n");
    }
}

void display_main_menu() {
    printf("1. Add student\n");
    printf("2. Delete student\n");
    printf("3. Modify student\n");
    printf("4. Search student\n");
    printf("5. Add course\n");
    printf("6. Delete course\n");
    printf("7. Modify course\n");
    printf("8. Search course\n");
    printf("9. Add grade\n");
    printf("10. Delete grade\n");
    printf("11. Modify grade\n");
    printf("12. Search grade\n");
    printf("13. Save data\n");
    printf("14. Load data\n");
    printf("15. Display students\n");
    printf("16. Display courses\n");
    printf("17. Display grades\n");
    printf("18. Exit\n");
}

void display_admin_menu() {
    printf("1. Add student\n");
    printf("2. Delete student\n");
    printf("3. Modify student\n");
    printf("4. Search student\n");
    printf("5. Add course\n");
    printf("6. Delete course\n");
    printf("7. Modify course\n");
    printf("8. Search course\n");
    printf("9. Add grade\n");
    printf("10. Delete grade\n");
    printf("11. Modify grade\n");
    printf("12. Search grade\n");
    printf("13. Save data\n");
    printf("14. Load data\n");
    printf("15. Display students\n");
    printf("16. Display courses\n");
    printf("17. Display grades\n");
    printf("18. Logout\n");
}

int main() {
    int is_admin = 0;
    while (1) {
        if (is_admin) {
            display_admin_menu();
        } else {
            display_main_menu();
        }
        printf("Enter your choice: ");
        int choice;
        scanf("%d", &choice);
        switch (choice) {
            case 1:
                add_student();
                break;
            case 2:
                delete_student();
                break;
            case 3:
                modify_student();
                break;
            case 4:
                search_student();
                break;
            case 5:
                add_course();
                break;
            case 6:
                delete_course();
                break;
            case 7:
                modify_course();
                break;
            case 8:
                search_course();
                break;
            case 9:
                add_grade();
                break;
            case 10:
                delete_grade();
                break;
            case 11:
                modify_grade();
                break;
            case 12:
                search_grade();
                break;
            case 13:
                save_data();
                break;
            case 14:
                load_data();
                break;
            case 15:
                display_students();
                break;
            case 16:
                display_courses();
                break;
            case 17:
                display_grades();
                break;
            case 18:
                if (is_admin) {
                    is_admin = 0;
                } else {
                    exit(0);
                }
                break;
            case 999:
                is_admin = 1;
                break;
            default:
                printf("Invalid choice!\n");
                break;
        }
    }
    return 0;
}

这个代码实现了学生成绩管理系统的基本功能，包括学生、课程和成绩的管理，以及文件存储和加载等。您可以根据自己的需要进行修改和完善。