#include "stack.h"
#include <stdlib.h>

// Create a new stack
struct stack *new_stack(int capacity)
{
	struct stack *pt = (struct stack *)malloc(sizeof(struct stack));
	pt->max_size = capacity;
	pt->top = -1;
	pt->items = (int *)malloc(sizeof(int) * capacity);
	return pt;
}

// Add a new item to a stack
void stack_push(struct stack *pt, int x)
{
	// Avoid a overflow by checking if the stack is full
	if (pt->top == pt->max_size - 1)
		err(0);
	// Add an element and increase the top index
	pt->items[++pt->top] = x;
}

// Get the topmost item of a stack
int stack_peek(struct stack *pt)
{
	// Check if the stack is empty
	if (pt->top == -1)
		err(1);
	return pt->items[pt->top];
}

// Remove the topmost item of a stack
int stack_pop(struct stack *pt)
{
	// Check for a stack underflow
	if (pt->top == -1)
		err(0);
	// Decrease the stack size by 1 and (optionally) return the popped element
	return pt->items[pt->top--];
}