Why we need to use # before ifndef?

Answer 1

if you mean that they both have # , yes

Answer 2

Because ifndef is a C preprocessor directive, like pragma, define or include, and every one of them starts with a #.

Answer 3

thank you all!

Answer 4

thank you very much!

Answer 5

Because it is syntax of C++ language

Answer 6

#ifndef is like #include?

Answer 7

and also you are a beautiful girl