看看这段程序，出错了怎么改，是建立一个链表的

# include <stdio.h>
# include <malloc.h>
# include <stdlib.h>
typedef struct st
{
int data;
struct st *pnext;
}node , * pnode ;
pnode ctrate_list(void)
{
int len,i,val;
pnode phead=(pnode)malloc(sizeof(node));
if(NULL==phead)
{
printf("分配失败，程序终止!\n");
exit(-1);
}
pnode ptail=phead;
ptail->data=NULL;
printf("请输入你要需要生成节点的个数:len=");
scanf("%d",&len);
for(i=0;i<len;i++)
{
printf("请输入第%d的节点的值:"，i+1);
scanf("%d",&val);
pnode pnew=(pnode)malloc(sizeof(node));
if(NULL==pnew)
{
printf("分配失败，程序终止!\n");
exit(-1);
}
pnew->data=val;
ptail->pnext=pnew;
pnew->pnext=NULL;
ptail=pnew;
}
return phead;
}