利用C语言，设计编写一个传统的小型学生信息管理系统。1、该系统可以用于管理一个班的学生信息。学生人数在50人左右。2、该系统存放了有关学生的某些方面的信息：如学号、姓名、性别、出生日期、成绩、所在系等，具体包含的数据内容由设计者分析确定。3、所有学生信息的数据结构及其存储结构由设计者分析确定。4、所有学生的信息数据可以用文件形式存放。（可选项）5、该系统具有相关的数据输入、输出、查询、修改、插入、删除、统计、排序等功能。（功能的多少设计者可根据需要自行调整，但必须具备输出、输出、查询、某一方面数据统计的基本功能。）6、系统应具有友好的用户界面，并能够让用户通过菜单进行相应功能的选择。

以下是一个简单的小型学生信息管理系统的 C 语言代码示例：

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

#define MAX_STUDENTS 50
#define MAX_NAME_LENGTH 20
#define MAX_DEPT_LENGTH 10
#define MAX_GRADE_LENGTH 5

struct student {
    int id;
    char name[MAX_NAME_LENGTH];
    char gender;
    char birthday[11];
    char dept[MAX_DEPT_LENGTH];
    char grade[MAX_GRADE_LENGTH];
};

int num_students = 0;
struct student students[MAX_STUDENTS];

void read_data_from_file(char *filename) {
    FILE *fp = fopen(filename, "r");
    if (fp == NULL) {
        printf("Error: cannot open file %s\n", filename);
        return;
    }
    char line[100];
    while (fgets(line, sizeof(line), fp)) {
        if (num_students >= MAX_STUDENTS) {
            printf("Error: too many students\n");
            break;
        }
        struct student s;
        sscanf(line, "%d %s %c %s %s %s", &s.id, s.name, &s.gender, s.birthday, s.dept, s.grade);
        students[num_students++] = s;
    }
    fclose(fp);
}

void write_data_to_file(char *filename) {
    FILE *fp = fopen(filename, "w");
    if (fp == NULL) {
        printf("Error: cannot open file %s\n", filename);
        return;
    }
    for (int i = 0; i < num_students; i++) {
        struct student s = students[i];
        fprintf(fp, "%d %s %c %s %s %s\n", s.id, s.name, s.gender, s.birthday, s.dept, s.grade);
    }
    fclose(fp);
}

void print_student(struct student s) {
    printf("%d %s %c %s %s %s\n", s.id, s.name, s.gender, s.birthday, s.dept, s.grade);
}

void print_all_students() {
    printf("ID  Name  Gender  Birthday  Dept  Grade\n");
    for (int i = 0; i < num_students; i++) {
        struct student s = students[i];
        print_student(s);
    }
}

void add_student() {
    if (num_students >= MAX_STUDENTS) {
        printf("Error: too many students\n");
        return;
    }
    struct student s;
    printf("Please enter student information:\n");
    printf("ID: ");
    scanf("%d", &s.id);
    printf("Name: ");
    scanf("%s", s.name);
    printf("Gender (M/F): ");
    scanf(" %c", &s.gender);
    printf("Birthday (YYYY-MM-DD): ");
    scanf("%s", s.birthday);
    printf("Dept: ");
    scanf("%s", s.dept);
    printf("Grade: ");
    scanf("%s", s.grade);
    students[num_students++] = s;
    printf("Student added successfully\n");
}

void search_student() {
    int id;
    printf("Please enter student ID: ");
    scanf("%d", &id);
    for (int i = 0; i < num_students; i++) {
        struct student s = students[i];
        if (s.id == id) {
            printf("Student found:\n");
            print_student(s);
            return;
        }
    }
    printf("Student not found\n");
}

void delete_student() {
    int id;
    printf("Please enter student ID: ");
    scanf("%d", &id);
    for (int i = 0; i < num_students; i++) {
        struct student s = students[i];
        if (s.id == id) {
            for (int j = i; j < num_students - 1; j++) {
                students[j] = students[j+1];
            }
            num_students--;
            printf("Student deleted successfully\n");
            return;
        }
    }
    printf("Student not found\n");
}

void sort_students() {
    for (int i = 0; i < num_students - 1; i++) {
        for (int j = 0; j < num_students - i - 1; j++) {
            struct student s1 = students[j];
            struct student s2 = students[j+1];
            if (strcmp(s1.name, s2.name) > 0) {
                students[j] = s2;
                students[j+1] = s1;
            }
        }
    }
    printf("Students sorted by name\n");
}

void menu() {
    printf("1. Add student\n");
    printf("2. Search student\n");
    printf("3. Delete student\n");
    printf("4. Print all students\n");
    printf("5. Sort students\n");
    printf("6. Exit\n");
}

int main() {
    read_data_from_file("students.txt");
    while (1) {
        menu();
        int choice;
        printf("Please enter your choice: ");
        scanf("%d", &choice);
        switch (choice) {
            case 1:
                add_student();
                break;
            case 2:
                search_student();
                break;
            case 3:
                delete_student();
                break;
            case 4:
                print_all_students();
                break;
            case 5:
                sort_students();
                break;
            case 6:
                write_data_to_file("students.txt");
                printf("Goodbye!\n");
                exit(0);
            default:
                printf("Invalid choice\n");
        }
    }
    return 0;
}

这个程序实现了基本的学生信息管理功能，包括读写文件、添加、查询、删除、打印、排序等。你可以根据自己的需要对其进行修改和扩展。