ll.c

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

struct A {
	int num;
	struct A* next;
}; 
//global variable

struct A *ptr = NULL; // for list tour
struct A *head = NULL;  // point list head(first) 
struct A *tail = NULL; // point list tail(end)

int Insert(int num);
void Delete_all(void);
int Delete(int num);
void Print(void);

int main(void)
{

	/*
	main 함수는 알아서 해서 내면 되
	*/
	
	Delete_all();
	return 0;
}

int Insert(int num)
{
	struct A* new = (struct A*)malloc(sizeof(struct A));//memory allocation
	struct A* pre = NULL;
	
	//memory allocation failed
	if (new == NULL)		return 0;
	
	// set node value
	new->num  = num;
	new->next = NULL;
	
	// the first Insert 
	if(head == NULL)
	{
		head = new;
		tail = new;
	}
	else
	{
		ptr = head;
		
		//search proper location
		while(ptr && (ptr->num < num))
		{
			pre = ptr;
			ptr = ptr->next;
		}
		
		//Insert
		if(ptr == head)
		{
			new->next = head;
			head = new;
		}
		else if(ptr == NULL)
		{
			tail->next = new;
			tail = new;
		}
		else
		{
			new->next = ptr;
			pre->next = new;
		}
	}
	return 1;	
}

void Delete_all(void)
{
	ptr = head;
	while(head)
	{
		ptr = head;
		head = head->next;
		free(ptr);
	}
}

int Delete(int num)
{
	struct A* pre = NULL;
	ptr = head;
	
	// search 
	while(ptr && (ptr->num != num))
	{
		pre = ptr;
		ptr = ptr->next;
	}
	//delete
	if(ptr == head)
	{
		head = head->next;
	}
	else if(ptr == tail)
	{
		tail = pre;
		pre->next = NULL;
	}
	else if(ptr == NULL)
	{// node is noneexistent
		return 0;
	}
	else
	{
		pre->next = ptr->next;
	}
	
	free(ptr);
	return 1;
}
void Print(void)
{
	ptr = head;
	while(ptr)
	{
		printf("%d -> ", ptr->num);
		ptr = ptr->next;
	}
	printf("NULL\n");
}