C语言：链表的循环，两种思考方法，第一种用select_1()实现，第二种用select_2()实现.

#include <stdio.h>
#include <stdlib.h>
#include<malloc.h>
struct s
{
int n;
struct s *next;
};
int i;
struct s *head, *tail;
void creat(m)
{
struct s *p, *p1;
head = NULL;
for(i=0; i<m; i++)
{
p = (struct s*)malloc(sizeof(struct s));
printf("Num %d: ", i+1);
scanf("%d", &p->n);
if(i==0)
head = p;
else
p1->next = p;
p1 = p;
}
tail = p1;
tail->next = head;
}
void select_1(int m)//第一种循环方法
{
struct s *p, *q;
int w=0;
p = tail;
while( p != p->next)
{
w++;
q = p, p = p->next;
if( w%m == 0)
{
printf("\nDelete the number: %d\n", p->n);
q->next = p->next;
free(p);
p = q->next; //不能写成 p = p->next,因为free(p),已释放p节点所占用的内存空间.
w++;
}
}
printf("\nOutput circular list the last node: %d\n\n", p->n);
}

void select_2(int m)//第二种循环循环方法
{
struct s *p, *q;
int w=0;
q = tail;
while( q != q->next)
{
w++;
p = q->next;
if( w%m == 0)
{
printf("\nDelete the number: %d\n", p->n);
q->next = p->next;
free(p);
}
else
q = q->next;
}
printf("\nOutput circular list the last node: %d\n\n", q->n);
}

void main()
{
int a, n, b, m;
printf("                                 \nPlease input the list nodes number: ");
scanf("%d", &a);
printf("\n");
creat(a);

printf("\nPlease input the interval: ");
scanf("%d", &n);
select_1(n);

printf("                                 \nPlease input the list nodes number: ");
scanf("%d", &b);
creat(b);
printf("\n");

printf("\nPlease input the interval: ");
scanf("%d", &m);
select_2(m);
}