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


typedef int element;
typedef struct StackNode{
	element item;
	struct StackNode* link;
}StackNode;

typedef struct{
	StackNode* top;
}LinkedStackType;

void init(LinkedStackType* s)
{
	s->top = NULL;
}

int is_empty(LinkedStackType* s)
{
	return (s->top == NULL);
}

int is_full(LinkedStackType* s)
{
	return 0;
}

void push(LinkedStackType* s , element item)
{
	StackNode* temp = (StackNode*)malloc(sizeof(StackNode));
	if(temp == NULL)
	{
		fprintf(stderr,"¸Þ¸ð¸®ÇÒ´ç¿¡·¯\n");
		return;
	}
	else
	{
		temp->item=item;
		temp->link=s->top;
		s->top=temp;
	}
}

element pop(LinkedStackType* s)
{
	if(is_empty(s))
	{
		fprintf(stderr,"½ºÅÃÀ̺ñ¾îÀÖÀ½\n");
		exit(1);
	}
	else
	{
		StackNode* temp=s->top;
		int item=temp->item;
		s->top = s->top->link;
		free(temp);
		return item;
	}
}
element peek(LinkedStackType* s)
{
	if(is_empty(s))
	{
		fprintf(stderr,"½ºÅÃÀ̺ñ¾îÀÖÀ½\n");
		exit(1);
	}
	else
	{
		return s->top->item;
	}
}

void main()
{
	LinkedStackType s;
	init(&s);
	push(&s,1);
	push(&s,2);
	push(&s,3);
	printf("%d\n",pop(&s));
	printf("%d\n",pop(&s));
	printf("%d\n",pop(&s));
	printf("%d\n",is_empty(&s));
}