2、 建立一个存储正整数的链表，链表包括头节点和尾节点，实现链表的输出、插入节点、和删除节点操作。

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

typedef struct Link
{
int num ;
struct Link *next;
}L;

void link( struct Link * head) //链表逆序
{
L *p, *q ,*temp, *temp2 ;
p = head ;
temp2 = q = head->next ;
while (q!=NULL)
{
temp = q->next ;
q -> next = p;
p = q ;
q = temp ;
}
temp2 ->next = NULL ;
head ->next = p ;
}

void output(struct Link *head)
{
L *p ;
p = head->next;
while (p != NULL)
{
printf("%d\n",p->num);
p = p->next;
}
}

void buildLink(struct Link * head)
{
L *p, *q ;
q = head;
int i;
for ( i = 1; i <= 5 ; i++)
{
p=(L *)malloc(sizeof(L));
p->num = i;
q->next=p;
q = p;
}
p->next = NULL;
}

int ListLength(L *head)
{
L*p;
int len;
for(p=head,len=