用C语言编写一个学生成绩管理系统，要求是使用链表作为结构，实现插入，删除，修改和查询功能

好的，我了解了你的要求。以下是用C语言实现学生成绩管理系统的代码：

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

// 定义学生结构体
typedef struct student {
    char name[20];
    int id;
    float score;
    struct student *next;
} Student;

// 新建学生节点
Student *new_student(char *name, int id, float score) {
    Student *stu = (Student*)malloc(sizeof(Student));
    strcpy(stu->name, name);
    stu->id = id;
    stu->score = score;
    stu->next = NULL;
    return stu;
}

// 插入学生节点
void insert_student(Student **head, Student *node) {
    if (*head == NULL) {
        *head = node;
        return;
    }
    Student *cur = *head;
    while (cur->next) {
        cur = cur->next;
    }
    cur->next = node;
}

// 删除学生节点
void delete_student(Student **head, int id) {
    if (*head == NULL) {
        return;
    }
    if ((*head)->id == id) {
        Student *tmp = *head;
        *head = (*head)->next;
        free(tmp);
        return;
    }
    Student *cur = *head;
    while (cur->next) {
        if (cur->next->id == id) {
            Student *tmp = cur->next;
            cur->next = tmp->next;
            free(tmp);
            return;
        }
        cur = cur->next;
    }
}

// 修改学生节点
void modify_student(Student **head, int id, float score) {
    if (*head == NULL) {
        return;
    }
    Student *cur = *head;
    while (cur) {
        if (cur->id == id) {
            cur->score = score;
            return;
        }
        cur = cur->next;
    }
}

// 查询学生节点
void search_student(Student *head, int id) {
    if (head == NULL) {
        return;
    }
    Student *cur = head;
    while (cur) {
        if (cur->id == id) {
            printf("学生姓名：%s，学号：%d，成绩：%.2f\n", cur->name, cur->id, cur->score);
            return;
        }
        cur = cur->next;
    }
}

int main() {
    Student *head = NULL;
    // 插入学生
    insert_student(&head, new_student("张三", 1001, 80));
    insert_student(&head, new_student("李四", 1002, 90));
    insert_student(&head, new_student("王五", 1003, 85));

    // 删除学生
    delete_student(&head, 1002);

    // 修改学生
    modify_student(&head, 1001, 85);

    // 查询学生
    search_student(head, 1003);

    return 0;
}

以上就是使用链表实现学生成绩管理系统的代码。注意，这里的代码只是一个简单的演示，实际应用中还需要完善其他功能，如输入输出、排序等。