Here I'm pointing out one of the main differences between the books and the movies.

1: Padma and Parvati
In the books Padma is in Ravenclaw and Parvati is in Gryffindor whereas in the movies both are in Gryffindor. I don't know why they did this in the movies but I think it's so both can get equal attention if you know what I mean...

2: Missing characters:
Here's a list of some if the missing characters that are in the books and not the movies:
Peeves
Charlie Weasley
Ludo Bagman
Bertha Jorkins
Professor Binns
Amdorwmda Tonks
Ted Tonks

3: PS
The third obstacle to get to the philosophers stone in the books is snakes potions. This is for some reason not shown in the movies.

4: The sorting:
In the books they say the person that's  getting sorted last name and then their first name whereas in the movies they say first to last. Also in the books Hannah Abbot gets sorted first but in the movies it was someone else.

5:
Why They didn't add peeves
Well, actually they did film him and stuff but thedirector didn't like the way he looked in camera so they cut him out

6: Diring the battle of the seven potters in deathly hallows (book) Hagrid and Harry are meant to land on the front yard of Tonks' parents house (andromeda and ted) whereas in the mice they land in the burrow.

7: They left out the deathday party in Philosphers Stone

8- Dobby is the one that's suggests gillyweed in the triwizard tournament not Neville

9: in the movies they didn't add Winky the house elf saving a spot for Barty Crouch jr in the quidditch World Cup

10: They didnt add S.P.E.W in the movies

This is just some of things that were left out in the movies and differences that I spotted while re watching all the movies. Honestly, I don't know he they would