ehsan
First comment, it's nothing to do with the C standard itself, so not
really topical here.
Second comment, on non-hosted environments (which is what embeded
systems tend to be) you do not necessarily have the standard C library
(you often have a subset of it, but it is not required).
As to system design, which you mention in the the subject line, that
varies drastically depending on the application whether it is embedded
or non-embedded, and has very little to do with C, since it is system
design (in part) which leads to the choice of programming language!
--
Flash Gordon