c语言链表，头插法和尾插法

#include 
#include 
#include 

typedef struct stdata{
    int e;
}data;

typedef struct stlink{
    data data;
    struct stlink* next;
}link;

struct link* create(){
    link* head = (link*)malloc(sizeof(link));
    memset(&head->data,0,sizeof(link));
    head->next = null;
    return head;
}

void head_insert(link* head,data e){
    link *ptemp,*pnew;
    if (head->data.e != 0){
        ptemp = head->next;
        pnew = (link*)malloc(sizeof(link));
        memcpy(&pnew->data,&e,sizeof(data));
        pnew->next = ptemp;
        head->next = pnew;
    }else{
        memcpy(&head->data,&e,sizeof(data));
    }
}

void nial_insert(link* head,data e){
    link *ptemp,*pnew;
    ptemp = head;
    if (head->data.e != 0){
        pnew = (link*)malloc(sizeof(link));
        memcpy(&pnew->data,&e,sizeof(data));
        while(ptemp->next != null)
            ptemp = ptemp->next;
        ptemp->next = pnew;
        pnew->next = null;
    }
    else{
        memcpy(&head->data,&e,sizeof(data));
    }
}

void dele(link* head,data e){
    link *pbefore = head;
    link *ptemp = head;
    while(ptemp->next != null){
        if (ptemp->data.e == e.e)
        {
            link *pdel = ptemp;
            pbefore->next = ptemp->next;
            pdel->next = null;
            free(pdel);
            return;
        }else{
            pbefore = ptemp;
            ptemp = ptemp->next;
        }
    }
    if (ptemp->data.e == e.e)
    {
        link *pdel = ptemp;
        pbefore->next = ptemp->next;
        pdel->next = null;
        free(pdel);
    }
}

void show(link* head){
    link *ptemp = head;
    while(ptemp->next != null){
        printf("%d \n",ptemp->data.e);
        ptemp = ptemp->next;
    }
    printf("%d \n",ptemp->data.e);
}

int main()
{
    link *head = create();
    data e1={1001},e2={1002},e3={1003},e4={1004};
    //head_insert(head,e1);
    //head_insert(head,e2);
    //head_insert(head,e3);
    //head_insert(head,e4);
    nial_insert(head,e1);
    nial_insert(head,e2);
    nial_insert(head,e3);
    nial_insert(head,e4);
    show(head);
    printf("dele------------\n");
    dele(head,e2);
    show(head);
    return 0;
}