C的动态链表建立

#include <stdio.h>
#define LENG sizeof(struct A)

struct A
{
	int num;
	char name[20];
	struct A *next;
};

struct A *head = NULL;			//头指针
struct A* lb();				//建立链表函数
void cha(struct A *head);		//查询函数
struct A* charu(struct A* head);	//插入函数
struct A* Delete(struct A*head,int x);	//删除函数

int main()
{
	int y;
	int x = 0; 
	
	while (1)
	{
		printf("(1)建立链表(2)查询链表(3)插入(4)删除(5)退出\n");
		scanf_s("%d", &y);
		switch (y)
		{
		case 1:head = lb();
			break;
		case 2:cha(head);
			break;
		case 3:head = charu(head);
			break;
		case 4:
			if (head == NULL)
			{
				printf("您的链表为空\n");
				break;
			}
			printf("请输入要删除的编号:");
			scanf_s("%d", &x);
			head = Delete(head,x);
			break;
		case 5:break;
		default:
			printf("输入错误请重新输入\n");
			continue;
		}
		if (y == 5)break;
	}
	system("pause");
	return 0;
}



struct A* lb()
{
	struct A *p1=NULL, *p2=NULL;
	int a, b, c;
	p1 = p2 = (struct A*)malloc(LENG);
	head = p1;
	printf("请输入编号:");
	scanf_s("%d", &p1->num);
	printf("请输入姓名:");
	scanf_s("%s", p1->name, 20);
	
	while (1)
	{
		p1 = (struct A*)malloc(LENG);
		printf("请输入编号0为结束:");
		scanf_s("%d", &a);
		if (a == 0)
		{
			free(p1);
			p2->next = NULL;
			break;
		}
		p1->num = a;
		printf("请输入姓名:");
		scanf_s("%s", p1->name, 20);
		p2->next = p1;
		p2 = p1;
	}
	return head;
}

void cha(struct A *head)
{
	while (1)
	{
		if (head == NULL)
		{
			printf("您的链表为空\n");
			break;
		}

		printf("%d\t%s\n", head->num, head->name);
		if (head->next == NULL)
		{
			break;
		}
		head = head->next;
	}
}

struct A* charu(struct A* head)
{
	struct A *p1, *p2, *p3;
	p1 = (struct A*)malloc(sizeof(struct A));
	p2 = head;
	printf("请输入编号:");
	scanf_s("%d", &p1->num);
	printf("请输入姓名:");
	scanf_s("%s", p1->name, 20);

	if (head->num > p1->num)
	{
		p1->next = head;
		return p1;
	}
	p3 = head;

	while (1)
	{
		if (p1->num < head->num)
		{
			p1->next = head;
			p3->next = p1;
			break;
		}
		else
		{
			p3 = head;
			if (head->next == NULL)
			{
				head->next = p1;
				p1->next = NULL;
				break;
			}
			head = head->next;
		}
	}
	return p2;
}

struct A* Delete(struct A*head,int x)
{
	struct A *p1,*p2;
	p1 = p2 = head;
	if (head->num == x)
	{
		p1 = head;
		head = head->next;
		free(p1);
		return head;
	}

	while (1)
	{
		if (head->num == x)
		{
			p1->next = head->next;
			break;
		}
		else
		{
			p1 = head;
			head = head->next;
		}
	}
	return p2;
}