why use a set c++ code example

Example 1: set in c++

#include <bits/stdc++.h>
#include <iostream>
#include <vector>
#include <algorithm>
#include <set>

using namespace std;
//set mentains internally the ascending order of these numbers
void setDemo()
{
	set<int> S;
	S.insert(1);
	S.insert(2);
	S.insert(-1);
	S.insert(-10);
	S.erase(1);//to remove an element
	
	//Print all the values of the set in ascending order
	for(int x:S){
		cout<<x<<" ";
	}
	
	//check whether an element is present in a set or not
	auto it = S.find(-1);//this will return an iterator to -1
	//if not present it will return an iterator to S.end()
	
	if (it == S.end()){
		cout<<"not Present\n";
	}else{
		cout <<" present\n";
		cout << *it <<endl;
	}
	//iterator to the first element in the set which is
	//greater than or equal to -1
	auto it2 = S.lower_bound(-1);
	//for strictly greater than -1
	auto it3 = S.upper_bound(-1);
	//print the contents of both the iterators
	cout<<*it2<<" "<<*it3<<endl;
}
	
int main() {
	setDemo();
	return 0;
}

Example 2: set c++

// constructing sets
#include <iostream>
#include <set>

bool fncomp (int lhs, int rhs) {return lhs<rhs;}

struct classcomp {
  bool operator() (const int& lhs, const int& rhs) const
  {return lhs<rhs;}
};

int main ()
{
  std::set<int> first;                           // empty set of ints

  int myints[]= {10,20,30,40,50};
  std::set<int> second (myints,myints+5);        // range

  std::set<int> third (second);                  // a copy of second

  std::set<int> fourth (second.begin(), second.end());  // iterator ctor.

  std::set<int,classcomp> fifth;                 // class as Compare

  bool(*fn_pt)(int,int) = fncomp;
  std::set<int,bool(*)(int,int)> sixth (fn_pt);  // function pointer as Compare

  return 0;
}