//本程序只給出了算法思想
//讀者可以自己完善本程序
struct	dlist
{
	float	data;
	struct 	dlist	*pre,*next;
}

//假設(shè)該循環(huán)雙鏈表的頭指針為head。實(shí)現(xiàn)本題功能的函數(shù)如下：
struct	dlist	*trans(stuct dlist* head)
{
	struct	dlist	*p,*q;
	p=head->next;
	q=head;
	while(p!=head)/*依次從左到右通過(guò)每個(gè)結(jié)點(diǎn)，對(duì)每個(gè)結(jié)點(diǎn)置pre值*/
	{
		p->pre=q;
		p=p->next;
		q=q->next;
	}
	head->pre=p;
	return(head);
}