You can start by creating a reply and showing what you did. DO NOT change your original post this will confuse people in the future.
You have presented an empty function which implies to most that you want someone to writ it for you. This is not likely to happen although you may get a generic function to give you an idea.
Better to post what you did and receive input about what is wrong.
By using "MAXSIZE" anywhere you refer to the size of the array and in for loops, should you want to change the size of the array you only have one place to do this. Should the array change shape you can use "MAXROW" and "MAXCOL". This save a lot of work having to check the whole program to make changes.
I changed your code a bit, following Handy Andy's advice.
( Try changing the 4 on line 11, to a higher number. )
Also shortened it a little. I did not add the coding to slide the numbers in the direction of the input, as I would like to see what ideas you come up with. I did add in check for legal moves, but didn't do anything other than inform the user it was a bad input, since the movement of the numbers is not yet implemented.
So... my deleted code wasn't entirely deleted for no reason. I had to do it, because it made it too long to fit in a post. Here's the pastebin for it: https://pastebin.com/6Q4K9b6s
Though, I warn you... it'll make your head spin. There's just so many if statements and all that jazz.
If either of you guys could help with that... it'd be godsend. Also, thank you for the condensed code, whitenite. Also, the whole constant thing would forever be 4, as the game board will always be 4x4. Thanks for the suggestion though, Andy.