Drop down box filter
 

My first drop down box in B1 has room numbers in it which are selected when I
choose a value from A1. I then have a drop down in C1 which has floor numbers
in it which are returned for each room number in B1.
I need to show a list in C1 which looks like this 1,0,-1 instead of one
which looks lilke this
11111111,000000000,-1-1-1-1-1-1-1, I'm not sure if this can be done or how
to do it, so coding help would be of great value.