Library in C

Different libraries provide differenet functionalities , check under installation directory of your compiler.

All libraries written in C?!.. Hundreds of million (or billions) lines of codes?!..
Probably you are multi-multi-millionaire: not all C libraries are freeware...

Or you prefer everything to be inside one super big library? In that case, your hello world program could become hundreds of megabyte in size because every single program has to link to that one and only library.

You are probably with the most common and known library of them all.. the Standard C Library.
It has good utilities you can use.. functions from headers <stdio.h>, <stdlib.h>, <string.h>, <time.h> will give you much power for your program.

Then you can either use libraries for OS-specific.. like the UNIX Library or smt like Win32 API for Windows.. however there are some platform-independent libraries written in C some of which are also free. Search google for them!

Or you prefer everything to be inside one super big library? In that case, your hello world program could become hundreds of megabyte in size because every single program has to link to that one and only library.

Even pathetic old 8-bitter toolchains had smarter libraries than that. Typically, it was bring in what's used (as opposed to a simple relocatable object file).