Problem with making a simple room

So i decided to write a program about mining out a room and replacing all the walls. It seemed to be working perfectly, until it got to the last wall or the 120 line of code. At that point any debuging or noticing the problems seemed to be impossible. I would like some insight why the 120th line does not work. Thanks in advance. (also, im a novice at computercraft, so the code might be rough around the edges)

The code : http://pastebin.com/ZwsAmcG5

Edit : Block type, which you want to use, go in the 15th slot, fuel goes in 16th slot

"k" is a number. "y" is a string. They'll hence never be identical.

y = tonumber(read())

That did the trick, thanks a lot !