Is there a way to receive bytes array, convert it to float and convert float to bytes and send them back?
An example of what will be received and what you expect to return would be good because at the moment I cannot make sense of your question.
Google "C++ Union". It's a way to take the same address space and refer to it in many different ways. So you could have the float in there and a 4 byte array. Since they occupy the same memory space it allows you to call it a float when you want it to be a float or a byte array when you want it to be a byte array.
Is this at all related to this other question of yours?
The general answer would be in here: http://www.gammon.com.au/serial