What is actuallly a "# "

Question

pre processor directive

Answer 1

every computer language defines some symbols and words which mean something special to the compiler of the language for example ' if()' in every language means that the next expression which is coming needs to be evaluated for true or false,
similarly when a while is encountered the compiler understands that there are some statements ahead need to be executed until some condition holds true but not every language implements them in the same way.
similarly python has defined #symbol to be start of a comment where as c and c++ have defined it as start of directives like #include , #define etc.

you can learn more about this in course called 'automata of computer languages' and 'compiler design '

Answer 2

It is very useful sign

https://en.m.wikipedia.org/wiki/Number_sign

Answer 3

It's comment symbol...
You can write your comments after this symbol in a single line, if you want to write two (or three, four...) lines comments, you must use the """...""" symbol...

Answer 4

But we write header file after #..
Not comment

Answer 5

I know but how????

Answer 6

depends on the language we are using

Answer 7

In C++ it is the Preprocessor command.
https://www.geeksforgeeks.org/cc-preprocessors/