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

#include "stack.h"

struct stack_element {
    int value;
    struct stack_element * next;
};

struct stack {
    struct stack_element * top;
};

struct stack * stack_new() {
    struct stack * this = malloc(sizeof(struct stack));
    if (this)
	this->top = 0;
    return this;
}

void stack_destroy(struct stack * this) {
    struct stack_element * e = this->top;
    while (e) {
	struct stack_element * tmp = e;
	e = e->next;
	free(tmp);
    }
    free(this);
}

int stack_push(struct stack * this, int v) {
    struct stack_element * e = malloc(sizeof(struct stack_element));
    if (e) {
	e->value = v;
	e->next = this->top;
	this->top = e;
	return 1;
    } else 
	return 0;
}

int stack_pop(struct stack * this) {
    struct stack_element * tmp = this->top;
    if (!tmp) {
	return STACK_UNDERFLOW;
    } else {
	int result = tmp->value;
	this->top = tmp->next;
	free(tmp);
	return result;
    }
}

void stack_print(const struct stack * this) {
    for(struct stack_element * e = this->top; e; e = e->next)
	printf("%d\n", e->value);
}