Book* CreateHead()
{
	Book *head,*p1,*p2;//定义三个指向Book的类,返回值给head
	p1=new Book;
	head=p1;
	p2=p1;//将三个结点一起在椎中创建
	cout<<"请输入图书编号,以0结束"<<endl;
	cin>>p1->num;
	if ( p1->num!=0 )
	{
		cout<<"请输入图书价格"<<endl;
		cin>>p1->price;
	}
	else
	{
		delete p1;
		p2=NULL;
		return head;
	}
	while ( p1->num!=0 )
	{
		p2=p1;//这步很重要,意思为将P2设为当前结点，然后用p1继续创建，用培p2->next指向p1
		p1=new Book;
		cout<<"请输入图书编号,以0结束"<<endl;
		cin>>p1->num;
		if ( p1->num!=0 )
		{
			cout<<"请输入图书价格"<<endl;
			cin>>p1->price;
		}
		p2->next=p1;
	}
	delete p1;
	p2->next=NULL;
	return head;
}