I am a bit confused by your first question:

I am working on the ADUC816QS,I am performing A/D conversion, now i am getting hex value for different input voltages, how to convert it to decimal,how to implement the floating point conversion.

As I understand it you have an ADC that is giving you a value proportional to a voltage. Presumably, this value is in binary and you wish to convert this to decimal representation for some purpose such as display. I don't understand where floating point comes into this.

If you are programming in C, the conversion is an elemetary programming problem for which you might choose to use printf().

For conversion to BCD, you may find the following useful:

http://www.programmersheaven.com/zone5/cat.../34429.htm

From BCD you may wish to convert to ASCII codes, see:

http://www.programmersheaven.com/zone5/cat.../32816.htm