When you come:
Ciao (= hello, informal, friendly) , Salve (= hello, less informal and formal)
When you leave:
Ciao (= Bye, informal, friendly), Arrivederci (= See you again, less informal and formal), Salve (= Goodbye, less informal and formal). Ci vediamo ( =See you, informal and formal). A presto, ci vediamo presto ( See you soon, informal and formal).