注意：

• 表头和头结点的区别，个人理解表头的元素因为没用到所以可不初始化
• 清空链表是仍保留链表的头结点，此时L！= NULL;而销毁链表是整个链表为空，L==NULL
• 表头指针和链表指针同时指向链表所在的内存，使用时要注意，尤其delete时。

可直接在vs2015上运行 

#include <iostream>
using namespace std;

typedef struct Node
{
	int Element;
	Node* Next;
}*Position, *SearchList, *Head;

SearchList MakeEmpty(SearchList L);
bool IsEmpty(SearchList L);
bool IsLast(Position L);
Position Find(int x, SearchList L);
Position FindPrevious(int x, SearchList L);//查找x的前驱
void DeleteNode(int x, SearchList L);
void InsertNode(int x, SearchList L);//前插
SearchList CreatList();//利用输入创建链表
void Traverse(SearchList L);

//清空链表，但仍保留头结点
SearchList MakeEmpty(SearchList L)
{
	//从第一个节点开始删除
	if (L == NULL)
		return NULL;
	Head pHead = L;
	L = pHead->Next;//第一个结点
	while (pHead->Next != NULL)
	{
		Position pTmp = new Node;
		pTmp = L;
		pHead->Next = pTmp->Next;
		L = L->Next;
		delete pTmp;//要最后delete,因为pTmp和L指向一个地址
	}
	return pHead;
}

bool IsEmpty(SearchList L)
{
	if (L == NULL)
		return true;
	else
		return false;
}

bool IsLast(Position L)
{
	if (L->Next == NULL)
		return true;
	else
		return false;
}

//返回x所在结点
Position Find(int x, SearchList L)
{
	if (L->Next == NULL)//空链表，但表头可能存在
		return nullptr;
	Head pHead = L;
	L = L->Next;
	while (L != NULL && L->Element != x)//顺序不能乱
		L = L->Next;
	return L;
}

Position FindPrevious(int x, SearchList L)
{
	if (L->Next == NULL)//空链表，但表头可能存在
		return nullptr;
	Head pHead = L;
	//L = L->Next;//第一个结点
	Position pTmp = nullptr;
	pTmp = new Node;
	pTmp = pHead;
	while (L->Next != NULL && L->Next->Element != x)
	{
		pTmp = L;
		L = L->Next;
	}
	if (L == NULL)
		return nullptr;
	return pTmp;
}

void DeleteNode(int x, SearchList L)
{
	Position xPre = FindPrevious(x, L);
	if (xPre)
	{
		Position xPos = xPre->Next;
		if (xPos->Next != nullptr)
		{
			Position xNext = xPos->Next;
			xPre->Next = xNext;
		}
		else
			xPre->Next = nullptr;
	}
	else
		cout << "没有要删除的元素,无需删除" << endl;
}

void InsertNode(int x, SearchList L)
{
	Head pHead = L;
	Position xPos = Find(x, L);
	if (xPos == NULL)
	{
		Position pTmp = new Node;
		pTmp->Element = x;
		pTmp->Next = pHead->Next;
		pHead->Next = pTmp;
		L = pHead;
	}
}

SearchList CreatList()
{
	Head pHead = nullptr;
	pHead = new Node;//表头

	SearchList L = pHead;
	L->Next = nullptr;//带表头的空链表
	cout << "Input data(-999 to quit):" << endl;
	int val = 0;
	while (1)
	{
		cin >> val;
		if (val == -999)
			break;
	
		Position isFind = Find(val, pHead);
		if (isFind)//重复元素不处理
			continue;

		Position newCell = nullptr;
		newCell = new Node;

		newCell->Element = val;
		newCell->Next = nullptr;

		L->Next = newCell;
		L = L->Next;//更新位置
	}
	return pHead;
}

void Traverse(SearchList L)
{
	if (L == NULL)
		cout << "链表为空" << endl;
	L = L->Next;
	while (L != NULL)
	{
		cout << L->Element << " ";
		L = L->Next;
	}
	cout << endl;
}

int main()
{
	char key;
	int num = 0;
	SearchList L = CreatList();
	Traverse(L);
	cout << "输入查找数字：";
	cin >> num;
	Position isFind = Find(num, L);
	if (isFind)
		cout << "查找成功，位置：" << isFind << endl;
	else
		cout << "未查找到" << endl;

	cout << "输入删除的数字：";
	cin >> num;
	DeleteNode(num, L);
	cout << "删除后的链表：" << endl;
	Traverse(L);
	
	cout << "输入插入的数字（重复不处理）：";
	cin >> num;
	InsertNode(num, L);
	cout << "插入后的链表：" << endl;
	Traverse(L);

	cout << "输入c让链表置空:" << endl;
	cin >> key;
	if (key == 'c' || key == 'C')
		L = MakeEmpty(L);
	if (IsEmpty(L))
		cout << "置空成功" << endl;

	system("pause");
}