Does sadness cause anger or anger cause sadness??

by my experiance i would say that its sadness that causes anger

yes it does but it depends on the scenario. Let's imagine a person crying and is in grief as someone important to them died. There sadness of this person's death causes anger by the growth of questioning why the person has died. Through this vengeance may also be lead through mixed emotions.

Vice versa, if you imagine a person being angry of being jailed, they might feel sadness to why they've done what they've done.

However, one can stay angry and one can stay sad without having any cause of sadness or anger.

This is theoretically speaking.

what was the