/* main.c -- program to demonstrate use of a stack */
#include <stdlib.h>
#include "stack.h"

struct stackElement {
    int item;
    struct stackElement * next;
};

/* methods the constructor needs to know about */
static void stackPush( Stack s, int i );
static int stackPop( Stack s );

/* constructor */
Stack newStack() {
    Stack new = malloc( sizeof( Stack* ) );
    new->pushMethod = &stackPush;
    new->popMethod = &stackPop;
    new->sp = NULL;
    return new;
}

/* methods */
static void stackPush( Stack s, int i ) {
    /* push i on stack s */
    struct stackElement * new = malloc( sizeof( struct stackElement ) );
    new->item = i;
    new->next = s->sp;
    s->sp = new;
}

static int stackPop( Stack s ) {
    /* pop an element from stack s and return it */
    struct stackElement * old = s->sp;
    int i = old->item;
    s->sp = old->next;
    free( old );
    return i;
}