双链表的创建与操作

#include<iostream>
/*
	双链表
*/
typedef int Elemtype;
typedef struct DNode{
	Elemtype data;		//数据域
	DNode *pre;			//前驱
	DNode *next;		//后继
}DNode,*DLinkList;
//头插法创建双链表
DLinkList createHeadDList() {
	DLinkList L = (DLinkList)malloc(sizeof(DNode));
	Elemtype e;
	L->next = NULL;
	L->pre = NULL;
	scanf("%d", &e);
	while (e != 999) {
		DNode *s = (DNode*)malloc(sizeof(DNode));
		s->data = e;
		s->next = L->next;
		if (L->next)
			L->next->pre = s;	//插入第一个结点时不需要这个操作
		s->pre = L;
		L->next = s;
		scanf("%d", &e);
	}
	return L;
}
//尾插法创建双链表
DLinkList createFootDList() {
	DLinkList L = (DLinkList)malloc(sizeof(DNode));
	Elemtype e;
	DNode *s,*r = L;
	L->pre = NULL;
	scanf("%d", &e);
	while (e != 999) {
		s = (DNode*)malloc(sizeof(DNode));
		s->data = e;
		r->next = s;
		s->pre = r;
		r = s;
		scanf("%d", &e);
	}
	r->next = NULL;
	return L;
}
//按序号查找结点
DNode * getElem(DLinkList L, int i) {
	if (i < 0) return false;
	if (i == 0) return L;
	int j = 1;
	DNode *p = (DNode*)malloc(sizeof(DNode));
	p = L->next;
	while (p&&j < i) {
		p = p->next;
		j++;
	}
	return p;
}
//插入
bool insDlist(DLinkList &L, int i, Elemtype e) {
	if (i <= 0) return false;
	DNode *p = getElem(L, i - 1);
	if(p) {
		DNode *q = (DNode*)malloc(sizeof(DNode));
		q->data = e;
		p->next->pre = q;
		q->pre = q;
		q->next = p->next;
		p->next = q;
		return true;
	}
	else
		return false;
}
//删除
bool delDlist(DLinkList &L, int i) {
	if (i <= 0) return false;
	DNode *p = getElem(L, i - 1);
	DNode *s = p->next;
	if (p&&s) {						//p和s都存在
		p->next = s->next;			//如果s为最后一个元素，p的后继指针指向空
		if (s->next)				//如果s后面还有元素
			s->next->pre = p;
		free(s);
		return true;
	}else
		return false;
}
//打印链表
void printList(DLinkList L) {
	DNode *p = L->next;
	while (p) {
		printf("%4d", p->data);
		p = p->next;
	}
	printf("\n");
}
int main() {
	//3 4 5 6 7 8 999
	//DLinkList L = createHeadDList();
	DLinkList L = createFootDList();
	if (insDlist(L, 3, 66)) {
		printList(L);
		printf("%d\n", getElem(L, 2)->data);
	}
	if (delDlist(L, 3))
		printList(L);
	system("pause");
}