can some1 help me on the codes for" design and development of an expert system for medical diagnosis.
and its program flow chart"

You need to be more specific. Your question is vary vague. What exactly are you been asked to do, what are your requirements, and what have you done so far.

If you post a more detailed and complete question, you will get better responses.

@Poster, is this a school assignment? if yes, then HECK NO!!!

If no, then tell us more so we can discuss the possibles on this as it sounds quite interesting!

An expert system takes the place of a real expert in a particular domain.
In this case a medical expert's diagnosist skills will be emulated by the software.
The patient will be asked a series of questions like " do you have fever" etc, and from the responses infer what the illness is , and give solution.
BayCity is that what your project is about?