#include <stdlib.h>

typedef struct stack stack;

typedef struct stack {
	char *tape;	
	int len;
	char *ptr;
} stack;

stack *push(stack *s, char c){
	if (s == NULL) {
		stack *outstack = malloc(sizeof(stack));	
		outstack->tape = malloc(1);
		outstack->tape[0] = c;
		outstack->ptr = outstack->tape;
		outstack->len = 1;
		return outstack;
	}
	s->len++;
	s->ptr++;
	s->tape = realloc(s->tape, s->len);
	*s->ptr = c;

	return s;
}

char pop(stack *s){
	char c = *s->ptr;
	*s->ptr = 0;
	s->len--;
	s->ptr--;
	s->tape = realloc(s->tape, s->len);

	return c;
}

char peek(stack *s){
	return *s->ptr;
}

void cleanstack(stack *s){
	free(s->tape);
	free(s);
}