[数据结构与算法]c语言单链表出现Segmentation fault，求助大神解决

这串代码在CodeBlocks运行无误，到学校的oj平台上就报段错误，不知道错到哪里了，请求指点。

这个题目就是单链表操作的一个集合。

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

typedef struct student
{
    long int num;
    float score;
    struct student *next;
}Node,*Link;

Link creatlink(void)
{
    Link head,node,rear;
    long int p;
    float q;
    head = (Link)malloc(sizeof(Node));
    head -> next = NULL;
    rear = head;
    while(scanf("%ld %f",&p,&q))
    {
        if(p == 0&&q == 0)
        {
            break;
        }
        node = (Link)malloc(sizeof(Node));
        node -> num = p;
        node -> score = q;
        rear -> next = node;
        rear = node;
    }
    rear -> next = NULL;
    return head;
}

void printlink(struct student *head)
{
    Link p;
    p = head -> next;
    while(p != NULL)
    {
        printf("%ld %.2f\n",p -> num,p -> score);
        p = p -> next;
    }
}

Link dellink(Link head,long int k)
{
    if(head == NULL||head -> next == NULL)
        exit(0);
    Link p,q;
    p = head -> next;
    q = head;
    while(p != NULL)
    {
        if(p -> num == k)
        {
            q -> next = p -> next;
            free(p);
        }
        else
        {
            q = p;
            p = p -> next;
        }
    }
    return head;
}

Link insertlink(Link head,Link stu)
{
    Link p,node,q;
    p = head;
    q = p -> next;
    while(q != NULL&&q -> num < stu -> num)
    {
        p = p -> next;
        q = p -> next;
    }
    if(q == NULL)
        p -> next = NULL;
    node = (Link)malloc(sizeof(Node));
    node -> num = stu -> num;
    node -> score = stu -> score;
    node -> next = p -> next;
    p -> next = node;
    return head;
}

void freelink(Link head)
{
    Link p;
    while(p != NULL)
    {
        p = head;
        head = head -> next;
        free(p);
    }
}

int main()
{
    struct student *createlink(void);
    struct student *dellink(struct student *, long);
    struct student *insertlink(struct student *, struct student *);
    void printlink(struct student *);
    void freelink(struct student *);
    struct student *head, stu;
    long del_num;
    head= creatlink();
    scanf("%ld", &del_num);
    head= dellink(head, del_num);
    scanf("%ld%f", &stu.num, &stu.score);
    head= insertlink(head, &stu);
    scanf("%ld%f", &stu.num, &stu.score);
    head= insertlink(head, &stu);
    printlink(head);
    freelink(head);
    return 0;
}