Implement OOPS concepts in code

i have created a program for System of banking process which is secured by login
only STAFF and CUSTOMER can access but OOPS concepts are not implemented much

my sir told that in this
inheritance
polymorphism
exception handling
virtual function
class for USER,STAFF,CUSTOMER

i made it portable so it can run on Linux and windows
can any one implement OOPS concept as much as possible
and as early too

code file is atttached in the link

#code is uploaded on git hub

https://github.com/anilsoni7/system