数据结构——指针仿真链表

#include<stdio.h>
#include<stdlib.h>

struct node{
	int data;
	node * next;
};

node * head = {NULL};

/*根据元素值删除元素*/
void del_by_data(int del_data)
{
	node * p = NULL;
	node * pre = NULL;
	p = head;
	while (p != NULL)
	{
		if (del_data == p->data)
		{
			if (pre != NULL)
			{
				pre->next = p->next;//删除之后改变结点的指向
			}
			if (p == head){
				head = p->next;//要删除的元素恰好是头节点
			}
			free(p);
			return;
		}
		pre = p;
		p = p->next;//遍历结点
	}
	return;
}

/*在链表末尾加入一个元素*/
void add_rear(int add_data)
{
	if (head != NULL)
	{
		node * add_point, *tmp_point;
		add_point = (node *)malloc(sizeof(node));//为插入的结点的分配内存
		add_point->data = add_data;
		add_point->next = NULL;
		tmp_point = head;//指向头结点
		while (tmp_point->next != NULL)
		{
			tmp_point = tmp_point->next;//遍历链表指向尾结点
		}
		tmp_point->next = add_point;//插入结点
	}
	else//链表为空
	{
		head = (node *)malloc(sizeof(node));
		head->data = add_data;
		head->next = NULL;
	}
}

/*在链表前端加入一个元素*/
void add_front(int add_data)
{
	if (head != NULL)
	{
		node * add_point = (node *)malloc(sizeof(node));
		add_point->data = add_data;
		add_point->next = head;
		head = add_point;
	}
	else
	{
		head = (node *)malloc(sizeof(node));
		head->data = add_data;
		head->next = NULL;
	}
}

void output()
{
	node *p = (node *)malloc(sizeof(node));
	p = head;
	while (p != NULL)
	{
		printf("%4d", p->data);
		p = p->next;
	}
	printf("\n");
}

int main()
{
	int ins, data;
	while (1)
	{
		printf("1.insert a value in front\n");
		printf("2.insert a value in rear\n");
		printf("3.delete a value\n");
		printf("4.quit\n");
		scanf("%d", &ins);
		switch (ins)
		{
			case 1:
				printf("please insert a value:");
				scanf("%d", &data);
				add_front(data);
				break;
			case 2:
				printf("please insert a value:");
				scanf("%d", &data);
				add_rear(data);
				break;
			case 3:
				printf("please insert a value:");
				scanf("%d", &data);
				del_by_data(data);
				break;
			default:
				goto loop;
		}
	}
	loop:
	 output();
	 system("pasue");
	 return 0;
}