I think you would do better to consider the code that Paul provided as an example and an opportunity to think about how it applies to your situation rather than something to just paste into your code and report back that it doesn't work.
You should ask yourself questions like
How wide do I want the number to be? e.g. "22.51345" would be 8 wide
What precision do I want it to have ? e.g. "-23.434" would be a precision of 3.
and
Is my buffer[] big enough to hold it?
Do I have room to put it on the LCD buffer[0], buffer[1], buffer[2],... buffer[width-1]