// Stack implemented as a linked list -- Pouya Larjani
// based on stack_as_linked_list.c by W. M. Farmer
#include <stdio.h>
#include <stdlib.h>
#include "stack.h"

// Make a new stack
stack bottom()
{
    stack s = (stack)malloc(sizeof(struct stack_s));
    s->top = NULL;
    s->height = 0;
    return s;
}

// Height of the stack
int height(stack s)
{
    return s->height;
}

// Top element of the stack
element top(stack s)
{
    if (s->height > 0)
        return s->top->data;
    fprintf(stderr, "Stack is empty\n");
    // printf(x) == fprintf(stdout, x)
    return NULL;
}

// Pop the top element of a stack
void pop(stack s)
{
    if (s->height == 0)
        fprintf(stderr, "Stack is empty\n");
    else
    {
        node n = s->top;
        s->top = n->below;
        s->height--;
        free(n);
    }
}

// Push an element to the top of the stack
void push(stack s, element data)
{
    // Make the new node
    node n = (node)malloc(sizeof(struct node_s));
    n->data = data;
    n->below = s->top;
    s->top = n;
    s->height++;
}

// Print a stack
void print_stack(stack s)
{
    printf("Stack: Height=%d", s->height);
    for (node n = s->top; n != NULL; n=n->below)
        printf(" -> [%s]", n->data);
    printf("\n");
}
/*
    for (init; cond; step)
    { ... }
    ==>
    
    init;
    while (cond)
    {
        ...;
        step;
    }
*/