#ifndef STACK_H
#define STACK_H

#include <stdlib.h>

typedef struct node {
    void *value;
    struct node *next;
} node;

typedef struct stack {
    node *head;
    int size;
} stack;

void push(stack *stk, void *val) {
    node *n = malloc(sizeof(node));
    n->value = val;
    n->next = stk->head == NULL ? NULL : stk->head; //either point to old head or become head
    stk->head = n; //become current head
    stk->size++;
}

void *pop(stack *stk) {
    if (stk->head == NULL) { //empty
        return NULL;
    }
    node *temp = stk->head; //temp pointer to old head
    void *val = temp->value; //get value
    stk->head = temp->next; //set new head
    free(temp); //free old head
    stk->size--;
    return val;
}

#endif