what do u mean by #include

Answer 1

The (#Include) Directive Is Used To Embed C++ Libraries Into Your .cpp File.

Answer 2

More precisely #include includes a file into an other file. That is a precompiler statement, nothing more. Usually we are including so called header files (.h), that contain declarations. Some declarations map to code in a precompiled libraries. And the linker will know which libraries to add to your application.
But you can live without having #include in your code. For example if you simply add the prototype of printf in your file, and you don't include stdio.h, printf will work just fine.