For the first question, I would avoid the word "encounter". It sounds like a euphemism. Also, it's too academic to describe a friendly meeting. "Let's say my friend and I met by chance, which made me happy. How can I say it to my friend?" "It was great running into you." or "It was great bumping into you." or "It's such a nice surprise to see you." For the second question, you need "to" in the sentence. "I called out to my friend walking across the street." or "I called out to my friend as she crossed the street."

Q1. I would express having enjoyed an encounter with another person in this way, "I really enjoyed meeting you!" If we had just met. And if I the person was my friend, I would say, "I really had fun hanging out with you!" Q2. I agree with Darren. "I called out to my friend walking across the street." You can also say, "I yelled to my friend across the street."

For the first question, Number 2 sounds best, it gives the idea that you enjoyed the meeting you just had. For question 2, the first answer is nearly correct, it should read, "I called out TO my friend walking across the street" Hope that helps you :)