private static double executaOperador(char op, double lhs, double rhs) throws InvalidOperator
	{
		switch (op) {
			case '+': return lhs + rhs;
			case '-': return lhs - rhs;
			case '*': return lhs * rhs;
			case '/': return lhs / rhs;
			default: throw new InvalidOperator(op);
		}
	}