Why only #include is used in first of ever program?

Question

??

Answer 1

because first step is to load library.
#include load the header file or library
that's why we use it as first line of program.

Answer 2

#include is like calling other libraries which contains lots of functions.

example -
You want to go a store and you have a wallet.

you have to put
money - "#include"

in your wallet so that you can...
buy - "function"

anything you want in the..
store - "compiler"

then you go home with your
goods - "program"