EP is correct :
Cases to consider
(1) x is positive ( but not an integer)
Then floor (x) - x will lie between (0, -1)
(2) x is a positve integer
Then floor (x) - x = 0
(3) x is negative, but not a negative integer
Then floor (x) - x will lie between (0, -1)
(4) x is a negative integer
Then floor (x) - x = 0
So.....just as EP said (-1, 0 ]