How do I learn how to control my emotions in public places?

If your emotions are leading you to be a danger in any way further help needs to be sought. If they are not you should recognise that they are your emotions. Take a breath and appreciate the way you are feeling. You are not alone, talking with someone else will help tremendously. You don't have to be the same as everyone else, be happy with who you are and be grounded in your own shoes. You have every right to walk in them, no one else does.

Try to get away from the trigger. But if the trigger has been set off, wait until you get to a secluded place before you let out your emotions. Count to 10 also, and do deep breathing until you calm down.

I sometimes have this issue to this day. I have a lot of trouble especially with anger and sadness. When in faced with confrontation I feel the tears welling in my eyes. I usually have to embarrassingly apologize that I cry and try to regain composure after that. I've found that with my anger I always stop and ask myself if it will matter 2 years down the road. If it will then I have a right but I need to walk away and decide how to fix the situation. If it won't bother me later in the future (such as a waitress getting my order wrong) then I will calm down and let it pass. I don't always have to be right and as long as the situation is fixed, then that's what matters. Everyone is human and we all make mistakes so I always have to remind myself that as well. When it comes to sadness I still have trouble with this. But I am able to distract myself with another thought and I can typically get back on track. I'll ask myself to do the multiplication tables or remember what I ate yesterday. It gives me time to compose myself and let go some of the emotion value. As long as you have a way to release your stress such as an activity such as writing, talking with friends or a sport then the emotions are easier to dissipate later as the day moves on.