In general using "" prioritizes headers in the current working directory over system headers. <> usually is used for system headers. It's comiler dependent.
Preprocessing directive of the form < >: # include <h-char-sequence> new-line
Compiler searches a sequence of implementation-defined places for a header identified uniquely by the specified sequence between the < and > delimiters, and causes the replacement of that directive by the entire contents of the header. How the places are specified or the header identified is implementation-defined.
A preprocessing directive of the form " ": # include "q-char-sequence" new-line
Compiler causes the replacement of that directive by the entire contents of the source file identified by the specified sequence between the " delimiters. The named source file is searched for in an implementation-defined manner. If this search is not supported, or if the search fails, the directive is reprocessed as if it read.
summary: Using the "" first checks your local directory, and if it doesn't find a match then moves on to check in the system path while using <> starts search directly with system headers.
