Need help with creating a function in a class

[EvanWeaksauce]

Hello, I am a computer science student. I am currently working on a "bag" class which is sort of a common sense answer to creating a random class with difference functions. I am attempting to create a "union" function which takes two bags ie: bag1 and bag2, adds all the items in both bags and creates a new bag ie: "bag3". For some reason I keep coming up with problems instead of solutions. Maybe it's the fact I just got done with 2 days of calculus. I don't know. My code is below. Both a main(source) and header file. Any help would be appreciated. Thanks in advance.

Header

#ifndef BAG_H
#define BAG_H

const int BAG_CAPACITY = 20;

template <typename T>
class Bag {
private:
	int count; // Number of items in the Bag
	T items[BAG_CAPACITY]; // Items in the Bag

	// Find index of a given item
	int findItem (const T& anEntry) const;
public:
	// Initialize the bag
	Bag () { count = 0; }

	// Get number of items in the bag
	int getCurrentSize () const { return count; }

	// Get an item from the bag using a zero-based index
	//	If index is invalid, returns a default item of type T
	T getItem (int index) const
		{ return index >= 0 && index < count ? items[index] : T(); }

	// Determine if bag is empty
	bool isEmpty () const { return count == 0; }

	// Add an item to the bag
	bool add (const T& newEntry);

	// Determine number of times item appears in the bag
	int getFrequencyOf (const T& anEntry) const;

	// Determine if the bag contains the given item
	bool contains (const T& anEntry) const
		{ return getFrequencyOf(anEntry) > 0; }

	// Clear all items from the bag
	void clear () { count = 0; }

	// Remove an item from the bag
	bool remove (const T& anEntry);
};

template <typename T>
bool Bag<T>::add (const T& newEntry) {
	if (count == BAG_CAPACITY)
		return false;
	items[count++] = newEntry;
	return true;
}

template <typename T>
int Bag<T>::getFrequencyOf (const T& anEntry) const {
	int freq = 0;
	for (int i = 0; i < count; i++)
		if (items[i] == anEntry)
			freq++;
	return freq;
}

template <typename T>
int Bag<T>::findItem (const T& anEntry) const {
	for (int i = 0; i < count; i++)
		if (items[i] == anEntry)
			return i;
	return -1;
}

template <typename T>
bool Bag<T>::remove (const T& anEntry) {
	if (!contains(anEntry))
		return false;
	for (int i = findItem(anEntry) + 1; i < count; i++)
		items[i-1] = items[i];
	count--;
	return true;
}

template <typename T>
void Bag<T>::union (const T&

#endif 

Main(source)

#include <fstream>
#include <iostream>
#include <string>
using namespace std;

#include "bag.h"

void add_item (Bag<string>& bag);
void init_bag (Bag<string>& bag, const string& fname);
void help ();
void remove_item (Bag<string>& bag);
void save_bag (const Bag<string>& bag, const string& fname);
void show_bag_detail (const Bag<string>& bag);
void show_bag_summary (const Bag<string>& bag);

int main () {

	// Declare and initialize bag.
	Bag<string> bag1, bag2;
	init_bag(bag1, "bag1.txt");
	init_bag(bag2, "bag2.txt");

	// Command loop...
	cout << endl;
	help();
	string command;
	do {
		cout << endl;
		cout << "bag1: "; show_bag_summary(bag1);
		cout << "bag2: "; show_bag_summary(bag2);
		cout << endl;
		cout << "Command: ";
		getline(cin, command);
		if (command == "add1") add_item(bag1);
		else if (command == "add2") add_item(bag2);
		else if (command == "remove1") remove_item(bag1);
		else if (command == "remove2") remove_item(bag2);
		else if (command == "detail1") show_bag_detail(bag1);
		else if (command == "detail2") show_bag_detail(bag2);
		else if (command == "diff12") ;// show_detail(bag1.difference(bag2))
		else if (command == "diff21") ;// show_detail(bag1.difference(bag2))
		else if (command == "intersect") ;// show_detail(bag1.intersection(bag2))
		else if (command == "union") ;// show_detail(bag1.union(bag2))
		else if (command != "exit")
			help();

	} while (command != "exit");

	// Save bag contents
	save_bag(bag1, "bag1.txt");
	save_bag(bag2, "bag2.txt");

//	system("pause");
	return 0;
}

void add_item (Bag<string>& bag){
	string item;
	cout << "Item to add: ";
	getline(cin, item);
	if (bag.add(item))
		cout << "Item added." << endl;
	else
		cout << "Failed to add item." << endl;
}

void help () {
	cout << "Valid commands: addN removeN detailN (N = 1 or 2)" << endl;
	cout << "                diff12 diff21 intersect union" << endl;
}

void init_bag (Bag<string>& bag, const string& fname) {

	// Open file of items. Exit if file not found.
	ifstream f(fname.c_str());
	if (!f) return;

	// Get all items from file and add to bag.
	string item;
	while (getline(f, item))
		bag.add(item);

	// Close file
	f.close();
}

void remove_item (Bag<string>& bag){
	string item;
	cout << "Item to remove: ";
	getline(cin, item);
//	if (bag.remove(item))
//		cout << "Item was removed." << endl;
//	else
//		cout << "Item was not found." << endl;
	cout << (bag.remove(item) ? "Item was removed." : "Item was not found.") << endl;
}

void save_bag (const Bag<string>& bag, const string& fname) {

	// Open file for saving bag contents.
	ofstream f(fname.c_str());
	if (!f) {
		cerr << "ERROR: Could not open mybag.txt for output." << endl;
		return;
	}

	// Save bag items
	for (int i = 0; i < bag.getCurrentSize(); i++)
		f << bag.getItem(i) << endl;

	// Close file
	f.close();
}

void show_bag_detail (const Bag<string>& bag) {
	show_bag_summary(bag);
	for (int i = 0; i < bag.getCurrentSize(); i++)
		cout << " - " << bag.getItem(i) << endl;
}

void show_bag_summary (const Bag<string>& bag) {
	if (bag.isEmpty())
		cout << "The bag is empty." << endl;
	else {
		int size = bag.getCurrentSize();
		if (size > 1)
			cout << "There are " << size << " items in the bag." << endl;
		else
			cout << "There is 1 item in the bag." << endl;
	}
}

[jmadsen]

Please provide more info on what you problem is. In any event, your union function should look something like:

template <typename T>
Bag<T> Bag<T>::union (const Bag<T>& rhs) const
{
    Bag<T> bag3;
    //... Loop over items in *this and add them to bag3
    //... Loop over items in rhs and add them to bag3
    return bag3;
}