Q: What's the difference between #include <> and #include "" ?
A: The <> syntax is typically used with Standard or system-supplied headers, while "" is typically used for a program's own header files. See also question 10.8b.
nice explanation by Kaz Kylheku
An article and a longer followup I posted in 1997 exploring some of the finer points which sometimes arise in deciding between #include ""and #include <>. (Warning: among the possibilities explored is that of using #include <> for your own header files under certain circumstances, a practice which is not standard and is not condoned by the readership of comp.lang.c.)