user17744: Due to impermanance of everything, Are there anything to be happy or sad about ? Even about dhamma ?
If something seems like to be happy, there are some reasons to not to be happy.

It is impermanant for sure. but also,
That happiness make sadness in the future (future includes next lives) (I need to be sure about this sententce, please mention about this in your answer)

Are enlightened people happy ? Or neither happy nor sad ?

user254: I think Buddhism recommends you focus on what's virtuous and moral instead of on what's feels pleasurable.
For example, lying, killing, stealing -- are all to be avoided -- and that's important.
Conversely, generosity, kindness, keeping your promises -- that's important too.
There is a word -- sukha -- which might be translated "happiness". It's used in contexts like the Sukhavagga.
I suspect it's a happiness conditioned or caused by an absence not by a presence -- for example not happiness because you have something ("a chocolate bar") but happiness because of not having something ("anger", "greed", "remorse").

user13375: Are there anything to care about in this universe?
Yes, you should care about other sentient beings and practice putting their well-being foremost in your mind. If you have no experience with this, then try practicing the four immeasurables.
Due to impermanance of everything, Are there anything to be happy or sad about?
Rejoice in other's happiness! Rejoice when other's wishes come true! Rejoice in other's sorrowless bliss! Rejoice in other's progress on the path of dhamma as this is the hope of the world!
That happiness make sadness in the future (future includes next lives)
You've got it completely and totally wrong friend. How can happiness make sadness in this life or in the next? The problem is sentient beings don't know what happiness is or how to get it. We chase after things that do not lead to happiness thinking they will and we shun things that do lead to happiness thinking they won't. We are like a dog tied to a pole and wound round-and-round... we pull harder and harder to get free, but only succeed in binding ourselves tighter to the very thing that makes us miserable. We are quite silly and ignorant.
Are enlightened people happy?
Of course! They are immeasurably happy. Indescribably happy. Happy to such an extent that it is impossible to conceive. How do we know this? Because in order to become enlightened they must work for countless lifetimes at accumulating and working at the causes of happiness! They must perfect all virtuous conduct! They must perfect all virtuous minds! Take them to their zenith! Imagine a mind as wide and deep as the ocean filled with the most altruistic and peaceful thoughts. With absolutely zero ill-will and focused on other's well-being to the limit. Such a mind... we cannot even begin to describe the happiness it entails!!
Or neither happy nor sad?
You need to work on discovering what happiness is and the causes and conditions of happiness. Fortunately, that is exactly what the dhamma teaches. Your confusion is caused by misunderstanding. Rest assured you have it blinkered, but keep working at it and working at it and working at it... don't stop! and you'll slowly unwind that leash holding you to the pole. 
Dhamma is the Ultimate Medicine. Buddha is the Ultimate Doctor. The Sangha are the Ultimate Nurses.
The disease is dhukka and unhappiness. The cure is happiness... immeasurably so!

user471: 
OP: Due to impermanance of everything, Are there anything to be happy or sad about ? Even about dhamma ?
Are enlightened people happy ? Or neither happy nor sad ?

From AN 9.34 (translated by Bhikkhu Sujato):

Ven: Sariputta: “Reverends, extinguishment (Nibbana) is bliss!
“sukhamidaṃ, āvuso, nibbānaṃ.
Ven. Udayi: “But Reverend Sāriputta, what’s blissful about it, since
  nothing is felt?”
“kiṃ panettha, āvuso sāriputta, sukhaṃ yadettha
  natthi vedayitan”ti?
Ven. Sariputta: “The fact that nothing is felt is precisely what’s
  blissful about it.
“Etadeva khvettha, āvuso, sukhaṃ yadettha natthi
  vedayitaṃ.

Sukha or happiness for an unenlightened person is experienced when encountering pleasant feelings (from the six senses, including thoughts and the intellect) or when encountering the cessation of painful feelings (from the six senses). But for an arahat, sukha or bliss (in this context) is experienced when encountering neutral feelings, no feelings and Nibbana.
Please see this answer for commentaries by Nyanaponika Thera. The supporting suttas are MN 44, SN 36.5 and AN 9.34.

17744: <p>Due to impermanance of everything, Are there anything to be happy or sad about ? Even about <strong>dhamma</strong> ?</p>

<p>If something seems like to be happy, there are some reasons to not to be happy.</p>

<ol>
<li>It is impermanant for sure. but also,</li>
<li>That <strong>happiness make sadness in the future (future includes next lives)</strong> (I need to be sure about this sententce, please mention about this in your answer)</li>
</ol>

<p>Are enlightened people happy ? Or neither happy nor sad ?</p>
 254: <p>I think Buddhism recommends you focus on what's virtuous and moral instead of on what's feels pleasurable.</p>

<p>For example, lying, killing, stealing -- are all to be avoided -- and that's important.</p>

<p>Conversely, generosity, kindness, keeping your promises -- that's important too.</p>

<p>There is a word -- <a href="https://en.wikipedia.org/wiki/Sukha" rel="nofollow noreferrer">sukha</a> -- which might be translated "happiness". It's used in contexts like the <a href="https://www.accesstoinsight.org/tipitaka/kn/dhp/dhp.15.budd.html" rel="nofollow noreferrer">Sukhavagga</a>.</p>

<p>I suspect it's a happiness conditioned or caused by an absence not by a presence -- for example not happiness because you have something ("a chocolate bar") but happiness because of not having something ("anger", "greed", "remorse").</p>
 13375: <p><strong>Are there anything to care about in this universe?</strong></p>

<p>Yes, you should care about other sentient beings and practice putting their well-being foremost in your mind. If you have no experience with this, then try <a href="https://thubtenchodron.org/meditation/03-prayers-practices/01-recitations/four-immeasurables/" rel="nofollow noreferrer">practicing the four immeasurables.</a></p>

<p><strong>Due to impermanance of everything, Are there anything to be happy or sad about?</strong></p>

<p>Rejoice in other's happiness! Rejoice when other's wishes come true! Rejoice in other's sorrowless bliss! Rejoice in other's progress on the path of dhamma as this is the hope of the world!</p>

<p><strong>That happiness make sadness in the future (future includes next lives)</strong></p>

<p>You've got it completely and totally wrong friend. How can happiness make sadness in this life or in the next? The problem is sentient beings don't know what happiness is or how to get it. We chase after things that <em>do not</em> lead to happiness thinking they will and we shun things that <em>do</em> lead to happiness thinking they won't. We are like a dog tied to a pole and wound round-and-round... we pull harder and harder to get free, but only succeed in binding ourselves tighter to the very thing that makes us miserable. We are quite silly and ignorant.</p>

<p><strong>Are enlightened people happy?</strong></p>

<p>Of course! They are immeasurably happy. Indescribably happy. Happy to such an extent that it is impossible to conceive. How do we know this? Because in order to become enlightened they must work for countless lifetimes at accumulating and working at the causes of happiness! They must perfect all virtuous conduct! They must perfect all virtuous minds! Take them to their zenith! Imagine a mind as wide and deep as the ocean filled with the most altruistic and peaceful thoughts. With absolutely zero ill-will and focused on other's well-being to the limit. Such a mind... we cannot even begin to describe the happiness it entails!!</p>

<p><strong>Or neither happy nor sad?</strong></p>

<p>You need to work on discovering what happiness is and the causes and conditions of happiness. Fortunately, that is exactly what the dhamma teaches. Your confusion is caused by misunderstanding. Rest assured you have it blinkered, but keep working at it and working at it and working at it... don't stop! and you'll slowly unwind that leash holding you to the pole. </p>

<p>Dhamma is the Ultimate Medicine. Buddha is the Ultimate Doctor. The Sangha are the Ultimate Nurses.</p>

<p>The disease is dhukka and unhappiness. The cure is happiness... immeasurably so!</p>
 471: <blockquote>
  <p><strong>OP:</strong> Due to impermanance of everything, Are there anything to be happy or sad about ? Even about dhamma ?</p>
  
  <p>Are enlightened people happy ? Or neither happy nor sad ?</p>
</blockquote>

<p>From <a href="https://suttacentral.net/an9.34/en/sujato" rel="nofollow noreferrer">AN 9.34</a> (translated by Bhikkhu Sujato):</p>

<blockquote>
  <p>Ven: Sariputta: “Reverends, extinguishment (Nibbana) is bliss!<br>
  <em>“sukhamidaṃ, āvuso, nibbānaṃ.</em></p>
  
  <p>Ven. Udayi: “But Reverend Sāriputta, what’s blissful about it, since
  nothing is felt?”<br>
  <em>“kiṃ panettha, āvuso sāriputta, sukhaṃ yadettha
  natthi vedayitan”ti?</em></p>
  
  <p>Ven. Sariputta: “The fact that nothing is felt is precisely what’s
  blissful about it.<br>
  <em>“Etadeva khvettha, āvuso, sukhaṃ yadettha natthi
  vedayitaṃ.</em></p>
</blockquote>

<p>Sukha or happiness for an unenlightened person is experienced when encountering pleasant feelings (from the six senses, including thoughts and the intellect) or when encountering the cessation of painful feelings (from the six senses). But for an arahat, sukha or bliss (in this context) is experienced when encountering neutral feelings, no feelings and Nibbana.</p>

<p>Please see <a href="https://buddhism.stackexchange.com/a/31463/471">this answer</a> for commentaries by Nyanaponika Thera. The supporting suttas are <a href="https://suttacentral.net/mn44/en/sujato" rel="nofollow noreferrer">MN 44</a>, <a href="https://suttacentral.net/sn36.5/en/sujato" rel="nofollow noreferrer">SN 36.5</a> and <a href="https://www.accesstoinsight.org/tipitaka/an/an09/an09.034.than.html" rel="nofollow noreferrer">AN 9.34</a>.</p>
