如何判断一个单链表是循环链表

typedef struct node
{

   int data;
   struct node *next;
}Node,*pnode;


 int is_Clink( pnode p)
 {
     pnode fastpoint,slowpoint;
    fastpoint=p;
    slowpoint = p;
    while(1)
    	{
    	  if(slowpoint==NULL||fastpoint==NULL)
		  	printf("This is linklist\n");
		  	return 1
	     slowpoint=slowpoint->next;
	     fastpoint=fastpoint->next->next;
	   if (slowpoint==fastpoint||fastpoint->next==slowpoint)
	   	printf("The si Clink\n");
	        return 0;
	   
    	}
 }
/*做一个小改进，优化一下代码结构如下：*/
  int is_Clink( pnode p)
 {
     pnode fastpoint,slowpoint;
    fastpoint=p;
    slowpoint = p;
    while(slowpoint &&fastpoint)
    	{
    	 
	     slowpoint=slowpoint->next;
	     fastpoint=fastpoint->next->next;
	   if (slowpoint==fastpoint||fastpoint->next==slowpoint)
	   	printf("The si Clink\n");
	        return 0;
	   
    	}
	printf("This is linklist\n");
	return 1
 }