C and C++

Question

Why someone should learn C when C++ exists?
In regard to every C code can compile in C++.

Answer 1

Are you sure when saying every c code compiles to c++ ?

Answer 2

Arsenic not all of them for example we can call a function in c before declaration but not in c++
Or using some c++ keywords as a name of a variable in c
But these differeces are not really important
I mean c++ has everything that c has.