Are the harry potter characters same from the beginning ?

I don't exactly know what you mean by this question. Yes, there are some characters that are present throughout the series and they are the same people throughout, but there are new characters too. And obviously characters evolve as they have new experiences, as they age and mature for the younger characters, and some characters are revealed more as the series develops, like Snape.

Well no. I mean, they are people, they grow up. Hermione turned out to be very caring for others with time, Ron become smarter and Harry was braver