stack(포인터 버전)

#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#define STACK_SIZE 100

/**** STACK ****/

/* external variables */
int contents[STACK_SIZE];
int *top_ptr = &contents[0];

void make_empty(void) {
	*top_ptr = 0;
}

bool is_empty(void) {
	return top_ptr == &contents[0];
}

bool is_full(void) {
	return top_ptr == &contents[STACK_SIZE];
}

void stack_underflow(void) {
	printf("stack underflow.\n");
	exit(EXIT_FAILURE);
}

void stack_overflow(void) {
	printf("stack overflow.\n");
	exit(EXIT_FAILURE);
}

void push(int i) {
	if (is_full())
		stack_overflow();
	else
		*top_ptr++ = i;
}

int pop(void) {
	if (is_empty())
		stack_underflow();
	else
		return *--top_ptr;
}