What extention is use for c++

Answer 1

Your question is not really clear, but I suppose you are referring to file extensions.

Source files: the most commonly used extension is '.cpp'.
Header files: '.h' or '.hpp'

Answer 2

Today this is the practice, most C++implementation files will use the ".cpp" extension and ".h" for the declaration of header files (the last one is still shared across most assembler and C compilers). There are other common extensions variations, such as, ".cc", ".C", ".cxx", and ".c++" for "implementation" code.