Setting a directional parameter

Hi!

Im trying to create a directional parameter within this file.

I have created a square curve line, and then divided it in its length - the number it is divided by changes. I now want to create lines from these points on my curve, and have them travel across to their opposite sides.

The problem I have is I can not figure out how to set a parameter that updates automatically so the lines know whether to travel   in +x, -x, +y or -y in direction in relation to their positioning.  

I think the Jpeg picture will make it more easy to understand.

I really appreiciate the help, and would be very gratefull if you could tell me if im just chasing a dream. . .

Cheers,

Dave!