C is a programming language originally developed for developing the Unix operating system.Then c++ ?

Explaining the differences between C and C++ in this thread is simply insufficient. It is better for you do look up other resources on the Internet.

http://www.cprogramming.com/tutorial/c-vs-c++.html
http://en.wikipedia.org/wiki/Compatibility_of_C_and_C%2B%2B
http://zarrata.com/durofy/computers/programming/10-major-differences-between-c-and-c/

C++ is the superset of C. One of the major difference is that C++ supports object-oriented programming while C does not. Hope you enjoy reading the references provided.