What to do next for Latin Square Program

[hockeynl]

I have to create a program that allows a user to fill in a (partial) Latin Square of order 4. You can use 0's to represent empty cells. The user will give the number to place, the row and column. The number should only be placed if it does not violate the properties of a partial Latin Square and it shouldn't rewrite numbers that have already been placed.

What I have so far:

https://gist.github.com/anonymous/5a66860c13eb8361b1aa

I am wondering what I should do next

I think I need to make functions for rows and columns (I was thinking for each rows and columns but then realized that it needs to work for any sized Latin Square)