*.h or *.hpp for C++ header files: which extension to choose?

Hi everyone! I'm new to C++ and developing my first small project — a class for working with matrices. I noticed that different projects and textbooks use different extensions for header files: some write `matrix.h`, others `matrix.hpp`. I got confused. I'm used to all header files in C having the `.h` extension. But C++ is a separate language, even though it's largely based on C. When I write a class definition, for example: ```cpp // matrix.h #ifndef MATRIX_H #define MATRIX_H class Matrix { public: Matrix(int rows, int cols); void print() const; private: int rows_, cols_; double* data_; }; #endif ``` ...it seems logical to me to use `.hpp` to explicitly indicate that this is C++, not C. But some colleagues say that `.h` is a