/*                                                                                        
 * stackops.c - singly linked list stack implementation
 *
 */
#include "mystack.h"

void push(int value)
{
    if (top == NULL)
    {   
        stack = (Node *) malloc (sizeof(Node));
        top = stack;
        stack -> value = value;
        stack -> next = NULL;
    }   
    else
    {   
        top -> next = (Node *) malloc (sizeof(Node));
        top -> next -> next = NULL;
        top = top -> next;
        top -> value = value;
    }   
}

Node * pop()
{
    Node *tmp, *tmp2;

    tmp = top;      // tmp points at top of stack
    tmp2 = stack;   // point tmp2 at bottom of stack

    if (tmp2 != NULL)   // on empty stack, don't do anything
    {
        if (tmp2 -> next != NULL) // two or more nodes in stack
        {
            while (tmp2 -> next -> next != NULL) // iterate to 2nd to last
            {
                tmp2 = tmp2 -> next;
            }
            tmp2 -> next = NULL;    // cap off our stack
            top = tmp2;             // tmp2 is the new top
        }
        else            // only one node in stack
        {
            stack = top = NULL;
        }
    }

    return(tmp);
}