stdio.h is a header file that is a part of the standard C library. It contains a number of routines used for standard input (usually from the keyboard) and output (usually to the console/terminal).
It can be included into your source.
It can be included into your source.
It can be included into your source.
The stdio.h file is used in c programs in order to import declarations of important functions and constants that are useful in doing input/output, using the library facilities of the compiler.
The latter is better.
No. That's a header file used for input and output.
Options/Compiler/Directories/Include - set the path of the include files.
Unity3d, Java, C, C++, C#, there are many programs they could use.
Platform dependent, possibly LIBC.LIB or something like that.
No, use java.
Their name, content and function.
You cannot, but you can use any text-editor to write C sources.