定义学生结构体struct Student类型如下： char id[10]; //学号 char Name[20];//姓名 double Score[3];//3门课程成绩 在主函数定义3个struct Student类型变量，并赋值，将3个变量插入到单链表的表头、表尾和指定位置用，C语言编写

好的，以下是C语言实现代码：

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

struct Student {
    char id[10];
    char Name[20];
    double Score[3];
    struct Student* next;
};

// 在单链表表头插入节点
void InsertAtHead(struct Student** head, struct Student* newStudent) {
    newStudent->next = *head;
    *head = newStudent;
}

// 在单链表表尾插入节点
void InsertAtTail(struct Student** head, struct Student* newStudent) {
    if (*head == NULL) {
        *head = newStudent;
    } else {
        struct Student* temp = *head;
        while (temp->next != NULL) {
            temp = temp->next;
        }
        temp->next = newStudent;
    }
}

// 在单链表指定位置插入节点
void InsertAtPos(struct Student** head, struct Student* newStudent, int pos) {
    if (pos <= 1) {
        InsertAtHead(head, newStudent);
    } else {
        struct Student* temp = *head;
        int i = 1;
        while (temp != NULL && i < pos - 1) {
            temp = temp->next;
            i++;
        }
        if (temp == NULL) {
            printf("指定位置不存在！\n");
        } else {
            newStudent->next = temp->next;
            temp->next = newStudent;
        }
    }
}

int main() {
    // 定义3个struct Student类型变量，并赋值
    struct Student* student1 = (struct Student*)malloc(sizeof(struct Student));
    strcpy(student1->id, "1001");
    strcpy(student1->Name, "张三");
    student1->Score[0] = 90;
    student1->Score[1] = 80;
    student1->Score[2] = 85;
    student1->next = NULL;

    struct Student* student2 = (struct Student*)malloc(sizeof(struct Student));
    strcpy(student2->id, "1002");
    strcpy(student2->Name, "李四");
    student2->Score[0] = 95;
    student2->Score[1] = 85;
    student2->Score[2] = 90;
    student2->next = NULL;

    struct Student* student3 = (struct Student*)malloc(sizeof(struct Student));
    strcpy(student3->id, "1003");
    strcpy(student3->Name, "王五");
    student3->Score[0] = 80;
    student3->Score[1] = 75;
    student3->Score[2] = 70;
    student3->next = NULL;

    // 将3个变量插入到单链表的表头、表尾和指定位置
    struct Student* head = NULL;
    InsertAtHead(&head, student1);
    InsertAtTail(&head, student2);
    InsertAtPos(&head, student3, 2);

    // 遍历单链表并输出每个节点的信息
    struct Student* temp = head;
    while (temp != NULL) {
        printf("学号：%s，姓名：%s，成绩：%.1f %.1f %.1f\n", temp->id, temp->Name, temp->Score[0], temp->Score[1], temp->Score[2]);
        temp = temp->next;
    }

    return 0;
}

输出结果与C++实现相同：

学号：1001，姓名：张三，成绩：90.0 80.0 85.0
学号：1003，姓名：王五，成绩：80.0 75.0 70.0
学号：1002，姓名：李四，成绩：95.0 85.0 90.0