sir can we convert c++ into c
C doesn't have object-oriented features, so if a C++ program doesn't use them, you can write an equivalent in C instead. Whether there's an automatic way to convert it, though, I doubt it.
totally impossible as functions on C++ does not run on C and vice versa.
C++ is based on C. The two are similar, but converting from one to the other is practically impossible. You would practically have to rewrite the entire program to accomplish this task.