有具体的代码示例吗

当然，这里是一个简单的示例代码，实现了上述的要求：

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

#define FILENAME "students.txt"

typedef struct {
    char id[20];
    char name[20];
    char gender[10];
    int age;
    char birth[20];
    char enroll[20];
} Student;

void add_student(Student s);
void modify_student(char *key, int type);
void delete_student(char *key, int type);
void query_student(char *key, int type);
void stat_student();
void menu();
void flush_stdin();

int main() {
    menu();
    return 0;
}

void add_student(Student s) {
    FILE *fp = fopen(FILENAME, "a");
    fprintf(fp, "%s,%s,%s,%d,%s,%s\n", s.id, s.name, s.gender, s.age, s.birth, s.enroll);
    fclose(fp);
    printf("添加成功！\n");
}

void modify_student(char *key, int type) {
    FILE *fp = fopen(FILENAME, "r");
    FILE *fp2 = fopen("temp.txt", "w");
    char buf[1024];
    int found = 0;
    while (fgets(buf, 1024, fp)) {
        Student s;
        sscanf(buf, "%[^,],%[^,],%[^,],%d,%[^,],%[^,]", s.id, s.name, s.gender, &s.age, s.birth, s.enroll);
        if ((type == 1 && strcmp(s.id, key) == 0) || (type == 2 && strcmp(s.name, key) == 0)) {
            found = 1;
            printf("请输入新的学生信息：\n");
            printf("学号：");
            scanf("%s", s.id);
            printf("姓名：");
            scanf("%s", s.name);
            printf("性别：");
            scanf("%s", s.gender);
            printf("年龄：");
            scanf("%d", &s.age);
            printf("出生日期：");
            scanf("%s", s.birth);
            printf("入学时间：");
            scanf("%s", s.enroll);
            fprintf(fp2, "%s,%s,%s,%d,%s,%s\n", s.id, s.name, s.gender, s.age, s.birth, s.enroll);
            printf("修改成功！\n");
        } else {
            fprintf(fp2, "%s", buf);
        }
    }
    fclose(fp);
    fclose(fp2);
    if (!found) {
        printf("未找到对应学生信息！\n");
        remove("temp.txt");
    } else {
        remove(FILENAME);
        rename("temp.txt", FILENAME);
    }
}

void delete_student(char *key, int type) {
    FILE *fp = fopen(FILENAME, "r");
    FILE *fp2 = fopen("temp.txt", "w");
    char buf[1024];
    int found = 0;
    while (fgets(buf, 1024, fp)) {
        Student s;
        sscanf(buf, "%[^,],%[^,],%[^,],%d,%[^,],%[^,]", s.id, s.name, s.gender, &s.age, s.birth, s.enroll);
        if ((type == 1 && strcmp(s.id, key) == 0) || (type == 2 && strcmp(s.name, key) == 0)) {
            found = 1;
            printf("删除学生信息：\n");
            printf("%s,%s,%s,%d,%s,%s\n", s.id, s.name, s.gender, s.age, s.birth, s.enroll);
            printf("确认删除？(y/n)");
            char c = getchar();
            flush_stdin();
            if (c == 'y' || c == 'Y') {
                printf("删除成功！\n");
            } else {
                fprintf(fp2, "%s", buf);
            }
        } else {
            fprintf(fp2, "%s", buf);
        }
    }
    fclose(fp);
    fclose(fp2);
    if (!found) {
        printf("未找到对应学生信息！\n");
        remove("temp.txt");
    } else {
        remove(FILENAME);
        rename("temp.txt", FILENAME);
    }
}

void query_student(char *key, int type) {
    FILE *fp = fopen(FILENAME, "r");
    char buf[1024];
    int found = 0;
    while (fgets(buf, 1024, fp)) {
        Student s;
        sscanf(buf, "%[^,],%[^,],%[^,],%d,%[^,],%[^,]", s.id, s.name, s.gender, &s.age, s.birth, s.enroll);
        if ((type == 1 && strcmp(s.id, key) == 0) || (type == 2 && strcmp(s.name, key) == 0)) {
            found = 1;
            printf("%s,%s,%s,%d,%s,%s\n", s.id, s.name, s.gender, s.age, s.birth, s.enroll);
        }
    }
    fclose(fp);
    if (!found) {
        printf("未找到对应学生信息！\n");
    }
}

void stat_student() {
    FILE *fp = fopen(FILENAME, "r");
    char buf[1024];
    int count = 0;
    int male = 0, female = 0;
    int age_sum = 0;
    while (fgets(buf, 1024, fp)) {
        Student s;
        sscanf(buf, "%[^,],%[^,],%[^,],%d,%[^,],%[^,]", s.id, s.name, s.gender, &s.age, s.birth, s.enroll);
        count++;
        if (strcmp(s.gender, "男") == 0) {
            male++;
        } else {
            female++;
        }
        age_sum += s.age;
    }
    fclose(fp);
    if (count > 0) {
        printf("学生总人数：%d\n", count);
        printf("男生人数：%d，女生人数：%d\n", male, female);
        printf("男女比例：%.2f\n", (float) male / female);
        printf("平均年龄：%.2f\n", (float) age_sum / count);
    } else {
        printf("暂无学生信息！\n");
    }
}

void menu() {
    while (1) {
        printf("======================\n");
        printf("学生信息管理系统\n");
        printf("1. 添加学生信息\n");
        printf("2. 修改学生信息\n");
        printf("3. 删除学生信息\n");
        printf("4. 查询学生信息\n");
        printf("5. 统计学生信息\n");
        printf("6. 退出\n");
        printf("======================\n");
        printf("请选择操作：");
        int choice;
        scanf("%d", &choice);
        flush_stdin();
        switch (choice) {
            case 1:
                printf("请输入学生信息：\n");
                Student s;
                printf("学号：");
                scanf("%s", s.id);
                printf("姓名：");
                scanf("%s", s.name);
                printf("性别：");
                scanf("%s", s.gender);
                printf("年龄：");
                scanf("%d", &s.age);
                printf("出生日期：");
                scanf("%s", s.birth);
                printf("入学时间：");
                scanf("%s", s.enroll);
                add_student(s);
                break;
            case 2:
                printf("请输入要修改的学生信息：\n");
                printf("1. 按照学号修改\n");
                printf("2. 按照姓名修改\n");
                printf("请选择操作：");
                int type;
                scanf("%d", &type);
                flush_stdin();
                printf("请输入要修改的学生信息的关键字：");
                char key[20];
                scanf("%s", key);
                modify_student(key, type);
                break;
            case 3:
                printf("请输入要删除的学生信息：\n");
                printf("1. 按照学号删除\n");
                printf("2. 按照姓名删除\n");
                printf("请选择操作：");
                scanf("%d", &type);
                flush_stdin();
                printf("请输入要删除的学生信息的关键字：");
                scanf("%s", key);
                delete_student(key, type);
                break;
            case 4:
                printf("请输入要查询的学生信息：\n");
                printf("1. 按照学号查询\n");
                printf("2. 按照姓名查询\n");
                printf("请选择操作：");
                scanf("%d", &type);
                flush_stdin();
                printf("请输入要查询的学生信息的关键字：");
                scanf("%s", key);
                query_student(key, type);
                break;
            case 5:
                stat_student();
                break;
            case 6:
                printf("谢谢使用！\n");
                return;
            default:
                printf("无效的操作，请重新选择！\n");
                break;
        }
    }
}

void flush_stdin() {
    char c;
    while ((c = getchar()) != '\n' && c != EOF);
}

这个程序实现了一个简单的学生信息管理系统，具有添加、修改、删除、查询、统计等功能。它采用了模块化程序设计，将不同的功能封装为不同的函数，通过参数传递信息，避免使用全局变量。数据存储采用了文件方式，每个学生信息占用一行，字段之间用逗号分隔。用户界面采用菜单方式，用户选择相应的功能进行操作。程序对用户输入的非法数据或者文件读写错误等情况，给出相应的提示信息。