Help with Operator Overloading

This is a Set ADT and I am having problems with overloading the + operator to do a union of two sets. What I was trying to do was load two vectors of integers to a temporary vector (removing the duplicates) but I have been unable to get it to work. Any suggestions please? Thanks.

Code:

#include <iostream>
#include <cstdlib>
#include <vector>

using namespace std ;

class Set 
{
   public:
    void add (int anItem) ;
    void remove (int anItem) ;
    int size () ;
    
    bool is_empty () ;
    bool has (int& the_target_item) ;
   
    
    friend ostream& operator << (ostream& OUTPUT, Set& aSet) ;
    friend istream& operator >> (istream& INPUT, Set& aSet) ;
    friend Set& operator + (Set& aSet, Set& anotherSet) ;   
   
   private:
    vector <int> theItems ;

};

int main ()
{

    
system ("Pause") ;
return 0 ;
}


void Set :: add (int anItem) 
{
 if (Set :: has(anItem))
 {
  //no-op
 }
 else
 {
  theItems . push_back (anItem) ;
 }  
}

void Set :: remove (int anItem) 
{
 for (int i = Set :: has (anItem); i < theItems . size () - 1; i++)
  {
   theItems[i] = theItems[i+1] ;
  }
 
 theItems . pop_back () ;
}

ostream& operator << (ostream& OUTPUT, Set& aSet) 
{
 OUTPUT << "Current Size: " <<  aSet . theItems . size() << "  " << endl ; 
 for (int i=0; i < aSet . theItems . size(); i++) 
 {
  OUTPUT << aSet . theItems[i] << " " ;
 }
  OUTPUT << endl ;
  return OUTPUT ;
}

istream& operator >> (istream& INPUT, Set& aSet) 
{
 int anItem ;
 cout << "Enter Items (Ctrl-z to End): " ;
 while ( cin >> anItem)
 {  
  aSet . add (anItem) ;
 }
 return INPUT ;
}

int Set :: size () 
{
 return theItems . size () ;
}

Set operator + (Set aSet, Set anotherSet) 
{
 vector <int> tmpVector ;
 tmpVector . push_back (aSet) ;
 tmpVector . push_back (anotherSet) ;
}

bool Set :: is_empty () 
{
 if (theItems . size () == 0)
 {
  return true ;
 }    
 else
 {
  return false ;
 }
}

bool Set :: has (int& the_target_item) 
{
 int i = 0 ;
 while ( i < theItems . size () && theItems [i] != the_target_item)
 {
  i++ ;
 }
 
 if ( i == theItems.size ( )  ) 	
 {		
  return false ;	
 }	
 else	
 {		
  return true ;	
 }   
}

Add some sort of index function that takes an int x and returns an int representing theItems[x]. Or overload operator [].

Then you need something like this (assuming you created a function called index):

Code:

for (each element in aSet) {
    if ( find( tmpVector.begin(), tmpVector.end(), aSet.index(i) ) == tmpVector.end() ) {
        add aSet(index) to tmpVector;
    }
}

repeat for anotherSet

If you keep the vectors sorted (or switch to std::set<int>) you can use std::set_union() to merge them.

There is also std::set_intersection() and std::set_difference().

For example this would be your operator+ :

Code:

Set Set::operator+(const Set& other) const{

	Set r;
	std::set_union(theItems.begin(),theItems.end(),other.theItems.begin(),other.theItems.end(),
				std::inserter(r.theItems,r.theItems.begin()));

	return r;
}