Set in C++ STL

Sets are a type of associative containers in which each element has to be unique because the value of the element identifies it. The values are stored in a specific order.  The value of the elements in a set cannot be modified once in the container (the elements are always const), but they can be inserted or removed from the container.

Syntax :
set<datatype> setname;

Member functions :

• Iterators:
  begin : Returns an iterator to the first element in the set (public member function )
  end : Return iterator to end (public member function )
  rbegin : Return reverse iterator to reverse beginning (public member function )
  rend : Return reverse iterator to reverse end (public member function )
  cbegin : Return const_iterator to beginning (public member function )
  cend : Return const_iterator to end (public member function )
  crbegin : Return const_reverse_iterator to reverse beginning (public member function )
  crend : Return const_reverse_iterator to reverse end (public member function )
• Capacity:
  empty : Test whether container is empty (public member function )
  size : Return container size (public member function )
  max_size : Return maximum size (public member function )
• Modifiers:
  insert : Insert element (public member function )
  erase : Erase elements (public member function )
  swap : Swap content (public member function )
  clear : Clear content (public member function )
  emplace : Construct and insert element (public member function )
  emplace_hint : Construct and insert element with hint (public member function )
• Observers:
  key_comp : Return comparison object (public member function )
  value_comp : Return comparison object (public member function )
• Operations:
  find : Get iterator to element (public member function )
  count : Count elements with a specific value (public member function )
  lower_bound : Return iterator to lower bound (public member function )
  upper_bound : Return iterator to upper bound (public member function )
  equal_range : Get range of equal elements (public member function )

// CPP program to demonstrate various functions of Set in C++ STL
#include <iostream>
#include <iterator>
#include <set>
//#include <bits/stdc++.h>

using namespace std;

int main()
{
	// empty set container
	set<int, greater<int> > s1;

	// insert elements in random order
	s1.insert(40);
	s1.insert(30);
	s1.insert(60);
	s1.insert(20);
	s1.insert(50);

	// only one 50 will be added to the set
	s1.insert(50);
	s1.insert(10);

	// printing set s1
	set<int, greater<int> >::iterator itr;
	cout << "\nThe set s1 is : \n";
	for (itr = s1.begin(); itr != s1.end(); itr++) {
		cout << *itr << " ";
	}
	cout << endl;

	// assigning the elements from s1 to s2
	set<int> s2(s1.begin(), s1.end());

	// print all elements of the set s2
	cout << "\nThe set s2 after assign from s1 is : \n";
	for (itr = s2.begin(); itr != s2.end(); itr++) {
		cout << *itr << " ";
	}
	cout << endl;

	// remove all elements up to 30 in s2
	cout << "\ns2 after removal of elements less than 30 "
			":\n";
	s2.erase(s2.begin(), s2.find(30));
	for (itr = s2.begin(); itr != s2.end(); itr++) {
		cout << *itr << " ";
	}

	// remove element with value 50 in s2
	int num;
	num = s2.erase(50);
	cout << "\ns2.erase(50) : ";
	cout << num << " removed\n";
	for (itr = s2.begin(); itr != s2.end(); itr++) {
		cout << *itr << " ";
	}

	cout << endl;

	// lower bound and upper bound for set s1
	cout << "s1.lower_bound(40) : \n"
		<< *s1.lower_bound(40) << endl;
	cout << "s1.upper_bound(40) : \n"
		<< *s1.upper_bound(40) << endl;

	// lower bound and upper bound for set s2
	cout << "s2.lower_bound(40) :\n"
		<< *s2.lower_bound(40) << endl;
	cout << "s2.upper_bound(40) : \n"
		<< *s2.upper_bound(40) << endl;

	return 0;
}
/*
Output : 
The set s1 is : 
60 50 40 30 20 10 

The set s2 after assign from s1 is : 
10 20 30 40 50 60 

s2 after removal of elements less than 30 :
30 40 50 60 
s2.erase(50) : 1 removed
30 40 60 
s1.lower_bound(40) : 
40
s1.upper_bound(40) : 
30
s2.lower_bound(40) :
40
s2.upper_bound(40) : 
60
*/