[noob][c++] std::set how do I use it?

I think this code is complicated enough for my purpose, in fact, I trimmed it a little bit just so that it seems simpler.


#include <iostream>
#include <set>

using namespace std;

int main()
{
      set<int, less<int> > s;
      set<int, less<int> >::iterator i;

       // what's the two line above?


       // this reads like an object instance "s" has two more numbers added to it.
      s.insert(4);
      s.insert(0);
       
      // this merely prints all, i think "i" is the index.

       cout << "The set contains the elements: " << endl;
      for (i=s.begin();  i !=s.end();  i++)
      {
      cout << *i  << endl;
      }
}

is each item in the set called a node?

this doesn't work :(


#include <iostream>
#include <set>

using namespace std;

int main()
{
      set<int> s;
      set<int> ::interator i;
      
      s.insert(4);
      s.insert(0);


      cout << "The set contains the elements: " << endl;
      for (i=s.begin();  i !=s.end();  i++)
      {
      cout << *i  << endl;
      }
}

ok, insert is to put a element/node into the ...set,

how do I access it?

can I arrange them?




#include <iostream>
#include <set>

using namespace std;

int main()
{
      set<int> s;
      set<int> ::interator i;
     
      s.insert(4);
      s.insert(0);


      cout << "The set contains the elements: " << endl;
      for (i=s.begin();  i !=s.end();  i++)
      {
      cout << *i  << endl;
      }
}

big to small

how do I display number of elements/node in the set?

     set<int, greater<int> > s;
      set<int, greater<int> >::iterator i;


set < //skip  >                   //  so this calls the set template?

what is

int, greater<int>    ?



and i am guessing that

in

      set<int, greater<int> > s;
      set<int, greater<int> >::iterator i;



s;          and
::iterator i;

are put in two lines following the big chunk because there can be more settings to the set<> right?

      cout << "The set contains the elements: " << endl;
      for (i=s.begin();  i !=s.end();  i++)
      {
      cout << *i  << endl;
      }



I don't get this part, how do I do this?

i = 5;
cout << s.i << endl;

show an item from the set given i = n;


like,

in that case

i expect

s.(0) = 4


or something

well, i ll admit (yet again)
that I am doing homework,
but i am trying to figure out the bits myself.




I think these two terms will help:

I am trying to learn the syntax of

its accessors and mutators.

i have to use set.

>>>> show an item from the set given i = n;

      set<int, greater<int> > s;
      set<int, greater<int> >::iterator iter;

      int n = 4;
      int i = 0;
      for (iter=s.begin(), i = 0;  iter !=s.end();  ++iter, ++i)
      {
            if (i == n)
           {
                cout << *iter  << endl;
                break;
           }
      }

You see a set is not very suitable for 'indexed' access. The purpose of a set is to get 'unique' items into an automatically sorted container:

     set<int> s;
     s.insert(5);
     s.insert(4);
     s.insert(1);

     set<int>::iterator iter = s.begin();
     cout << *iter;  // shows 1

     *iter = 6;    // update first element

      iter = s.begin();
      cout << *iter;  // shows 4

Note, the set::iterator::operator*() is an overloaded derefencere operator. It isn't a dereference of a 'pointer' as set::iterator is a class type and not a pointer. But of course it is 'willingly' made that you can use an iterator like a pointer.