#include <stdio.h>		enum Boolean { False, True };		template <class Type> class List;					//鏈表類的前視定義		template <class Type> class ListIterator;				//鏈表結(jié)點(diǎn)類的前視定義		template <class Type> class ListNode {					//鏈表結(jié)點(diǎn)類的類聲明		friend class List <Type>;							//友元		friend class ListIterator <Type>;					//友元		public:		   ListNode ( const Type value ) : data (value), link (NULL) { }		   //………		private:		   Type data;		   ListNode<Type> *link;		};		template <class Type> class List {					//鏈表類的類聲明		public:		   friend class ListIterator<Type>;		   List ( const Type value) { last =first = new ListNode<Type> (value) ; }	//構(gòu)造函數(shù)		   int sum ();		   void Add ( const Type value ) ;		   //………		private:		   ListNode<Type> *first, *last;		};		template <class Type> class ListIterator {				//鏈表游標(biāo)類的類聲明		public:		   ListIterator ( const List<Type> & l ) : list (l), current (l.first) { }		   Boolean NotNull ( );		   Boolean NextNotNull ( );		   ListNode<Type>* First ( );		   ListNode<Type>* Next ( );		private:		   const List<Type> & list;						//引用一個(gè)已存在的鏈表		   ListNode<Type> *current;						//指向鏈表中的一個(gè)結(jié)點(diǎn)		};		template <class Type> Boolean ListIterator<Type>::NotNull ( ) {		//檢查鏈表中當(dāng)前元素是否非空		   if ( current != NULL ) return True; 					//鏈表當(dāng)前結(jié)點(diǎn)指針非空		   else return False;		}		template <class Type> Boolean ListIterator<Type>::NextNotNull ( ) {		//檢查鏈表中下一元素是否非空		   if ( current != NULL && current->link != NULL ) return True;		   else return False;		}		template <class Type> ListNode<Type>* ListIterator<Type>::First ( ) {		//返回指向鏈表中表頭結(jié)點(diǎn)的指針		   if ( list.first->link != NULL ) { current = list.first; }		   else { current = NULL; }		   return current ;		}		template <class Type> ListNode<Type>* ListIterator<Type>::Next ( ) {		//返回指向鏈表中下一個(gè)結(jié)點(diǎn)的指針		   if ( current != NULL && current->link != NULL ) { current = current->link; }		   else { current = NULL; }		   return current;		}		int List<int> :: sum ()  {		   ListIterator<int> li ( *this );							//定義對(duì)象li為操作鏈表對(duì)象l的游標(biāo)對(duì)象		   if ( ! li.NextNotNull ( ) ) return 0;					//空鏈表, 返回0		   int retvalue = li.First ( ) ->data ;						//取得第一個(gè)元素的值		   while ( li.NextNotNull ( ) ) retvalue += li.Next ( ) ->data;		//看是否下一個(gè)結(jié)點(diǎn)存在，若有, 累加		   return retvalue;		}		template <class Type> void List<Type>::Add(const Type value) {		   last->link = new ListNode<Type> (value);		   last = last->link;		}