7 Segment display dimming

You seem to be trying to do this from scratch. I haven't analysed the code, but you would be better off using one of the established libraries.

The code is unclear - I am not sure what much of it is trying to do (a few comments would help). There are obvious errors - in particular the incorrect use of sizeof() which is a common error.

I use the following http://playground.arduino.cc/Main/SevenSegmentLibrary

This just requires a single call to set the digits to be displayed and includes a Brightness call.