本人初学C，编了一段练习结构和联合知识方面的代码。但debug时出现     c programme received signal sigsegv segmentation fault
不明其原因，请有时间的前辈指点。
代码如下（本人初学，代码风格很挫请见谅）
目的：输入每个学生的学号，姓名，英语数学物理设计四门成绩。然后输出每个学生的各项信息。

#include <stdio.h>
#include "stdlib.h"
struct xinxi{
    int xuehao;
    char *xingming;
    float yingyu;
    float shuxue;
    float wuli;
    float sheji;
    struct xinxi *p;
};
void create_list (struct xinxi **headp);
int main(void)
{
    struct xinxi *head=NULL,*pp;

    create_list(&head);
    pp=head;
    while(pp){
        printf ("xuehao:%d\tname:%s\n",pp->xuehao,pp->xingming);
        printf ("yingyu:%f\tshuxue:%f\twuli:%f\tsheji:%f\n",pp->yingyu,pp->shuxue,pp->wuli,pp->sheji);      /* 输出数据域的值 */
        pp=pp->p;
    }
    printf("\n");

    return 0;
}
void create_list(struct xinxi **headp)
{
        struct xinxi * loc_head=NULL,*tail;
        int xuanze;

        loc_head=(struct xinxi *)malloc(sizeof(struct xinxi));
        printf ("xuehao,name:\t");
        scanf  ("%d,%s",&loc_head->xuehao,loc_head->xingming);
        getchar();
        printf ("yingyu,shuxue,wuli,sheji: ");
        scanf  ("%f,%f,%f,%f",&loc_head->yingyu,&loc_head->shuxue,&loc_head->wuli,&loc_head->sheji);
        getchar();
        loc_head->p=NULL;
        printf ("if you want to enter next one input '1'\n " );
        scanf ("%d",&xuanze);

        while(1==xuanze)
        {
            tail=(struct xinxi *)malloc(sizeof(struct xinxi));
            tail->p=loc_head;
            printf ("xuehao,name:\t");
            scanf  ("%d,%s",&tail->xuehao,tail->xingming);getchar();
            printf ("yingyu,shuxue,wuli,sheji: ");
            scanf  ("%f,%f,%f,%f",&tail->yingyu,&tail->shuxue,&tail->wuli,&tail->sheji);getchar();
            loc_head=tail;
            printf ("if you want to enter next one input 1\n " );
            scanf ("%d",&xuanze);
        }


    *headp=loc_head;
}

    struct xinxi *head=NULL,*pp;

    create_list(&head);
传了空指针的指针进去目的是？

我觉得应该给该指针初始化一下，所以用NULL赋值了。