Syntax:
#include <set> set(); set( const set& c ); ~set();
Every set has a default constructor, copy constructor, and destructor.
The default constructor takes no arguments, creates a new instance of that set, and runs in constant time. The default copy constructor runs in linear time and can be used to create a new set that is a copy of the given set c.
The default destructor is called when the set should be destroyed.