#include <stdio.h>
#include <string.h>

void bar(void(*callback)(int))
{
	callback(getc(stdin));
}

int foobar()
{
	__label__ fin_error, fin_multiplex;
	void *finishp = &&fin_ok;
	int value = 0;

	void foo(int ch) {
		if ( ch < 0 ) goto fin_error;
		if ( ch == '\n' ) goto fin_multiplex;
		if ( ch < '0' || ch > '9' ) finishp = &&fin_error;
		value = value * 10 + ch - '0';
	}

	while (1) bar(foo);

fin_multiplex:
	goto *finishp;

fin_error:
	return -1;

fin_ok:
	return value;
}

int main()
{
	int tmp = foobar();
	printf("%d = 0x%X\n", tmp, tmp);
	return 0;
}