Doubly Linked List c++ implementing with a Class - c++

Question

I am trying to create a doubly linked list:
class DblLinkedBag
{
private:
struct node{
string data;
node* next;
node* prev;
}*start=NULL;
int itemCount;
string item;
node *head;
node *tail;
public:
DblLinkedBag();
~DblLinkedBag();
int getCurrentSize();
bool isEmpty();
string add(string value);
bool remove(string item);
void clear();
bool contains(string target);
int getFrequencyOf();
string toVector();
string getItem();
void display();
};
So far, I have gotten add, isEmpty, getCurrentSize and clear to work. Now I just need the rest to work and I am having a hard time. My professor gave us a requirement that the class had to be implemented like this:
#include <iostream>
#include <string>
#include "LinkedBag.h"
using namespace std;
void displayBag(LinkedBag<string>& bag)
{
cout << "The bag contains " << bag.getCurrentSize()
<< " items:" << endl;
vector<string> bagItems = bag.toVector();
int numberOfEntries = (int) bagItems.size();
for (int i = 0; i < numberOfEntries; i++)
{
cout << bagItems[i] << " ";
} // end for
cout << endl << endl;
} // end displayBag
void copyConstructorTester()
{
LinkedBag<string> bag;
string items[] = {"zero", "one", "two", "three", "four", "five"};
for (int i = 0; i < 6; i++)
{
cout << "Adding " << items[i] << endl;
bool success = bag.add(items[i]);
if (!success)
cout << "Failed to add " << items[i] << " to the bag." << endl;
}
displayBag(bag);
LinkedBag<string> copyOfBag(bag);
cout << "Copy of bag: ";
displayBag(copyOfBag);
cout << "The copied bag: ";
displayBag(bag);
} // end copyConstructorTester
void bagTester()
{
LinkedBag<string> bag;
cout << "Testing the Link-Based Bag:" << endl;
cout << "isEmpty: returns " << bag.isEmpty()
<< "; should be 1 (true)" << endl;
displayBag(bag);
string items[] = {"one", "two", "three", "four", "five", "one"};
cout << "Add 6 items to the bag: " << endl;
for (int i = 0; i < 6; i++)
{
bag.add(items[i]);
} // end for
displayBag(bag);
cout << "isEmpty: returns " << bag.isEmpty()
<< "; should be 0 (false)" << endl;
cout << "getCurrentSize: returns " << bag.getCurrentSize()
<< "; should be 6" << endl;
cout << "Try to add another entry: add(\"extra\") returns "
<< bag.add("extra") << endl;
cout << "contains(\"three\"): returns " << bag.contains("three")
<< "; should be 1 (true)" << endl;
cout << "contains(\"ten\"): returns " << bag.contains("ten")
<< "; should be 0 (false)" << endl;
cout << "getFrequencyOf(\"one\"): returns "
<< bag.getFrequencyOf("one") << " should be 2" << endl;
cout << "remove(\"one\"): returns " << bag.remove("one")
<< "; should be 1 (true)" << endl;
cout << "getFrequencyOf(\"one\"): returns "
<< bag.getFrequencyOf("one") << " should be 1" << endl;
cout << "remove(\"one\"): returns " << bag.remove("one")
<< "; should be 1 (true)" << endl;
cout << "remove(\"one\"): returns " << bag.remove("one")
<< "; should be 0 (false)" << endl;
cout << endl;
displayBag(bag);
cout << "After clearing the bag, ";
bag.clear();
cout << "isEmpty: returns " << bag.isEmpty()
<< "; should be 1 (true)" << endl;
} // end bagTester
int main()
{
copyConstructorTester();
bagTester();
return 0;
} // end main
So far this is what I have.
#include <iostream>
#include <string>
#include <vector>
#include <stdio.h>
#include <stdlib.h>
using namespace std;
class DblLinkedBag
{
private:
struct node{
string data;
node* next;
node* prev;
}*start=NULL;
int itemCount;
string item;
node *head;
node *tail;
public:
DblLinkedBag();
~DblLinkedBag();
int getCurrentSize();
bool isEmpty();
string add(string value);
bool remove(string item);
void clear();
bool contains(string target);
int getFrequencyOf();
string toVector();
string getItem();
void display();
};
DblLinkedBag::DblLinkedBag()
{
itemCount=0;
item;
}
string DblLinkedBag::add(string value)
{
node* n;
cout<<itemCount<<endl;
if(itemCount==0)
{
n=new node;
n->data=value;
n->prev=NULL;
head=n;
tail=n;
}
if(itemCount>0 && itemCount<7)
{
n= new node;
n->data=value;
n->prev=tail;
tail->next=n;
tail=n;
}
itemCount++;
return value;
}
void DblLinkedBag::display()
{
struct node* temp=start;
while(temp != NULL)
{
cout<<temp->data<<endl;
temp=temp->next;
}
}
int DblLinkedBag::getCurrentSize()
{
return itemCount;
}
bool DblLinkedBag::contains(string target)
{
//need help here, supposed to tell if the linked list contains a certain //string
bool found= false;
node* curPtr=start;
int i=0;
while (!found && (curPtr!=NULL)&& (i<itemCount))
{
if(target==curPtr->data)
{
found=true;
}
else
{
i++;
curPtr=curPtr->next;
}
}
return found;
}
bool DblLinkedBag::isEmpty()
{
bool empty;
if (itemCount==0)
{
empty=true;
}
else
empty=false;
return empty;
}
void DblLinkedBag::clear()
{
node* nodeToDelete=start;
while (start != NULL)
{
start=start->next;
nodeToDelete->next=NULL;
delete nodeToDelete;
}
itemCount=0;
}
bool DblLinkedBag::remove(string item)
{
//need help here
}
string DblLinkedBag::toVector()
{
//need help here this is supposed to send the linked list to a vector
vector<string> vct;
node* curPtr= start;
int counter = 0;
while ((curPtr != NULL) && (counter < itemCount))
{
vct.push_back(curPtr->data);
curPtr = curPtr->next;
counter++;
}
}
int DblLinkedBag::getFrequency()
{//supposed to show how many of a certain item are in the linked list
DblLinkedBag::~DblLinkedBag()
{
}
Any help implementing these class functions to create the other functions my professor gave me would be appreciated, I have tried all different kinds of implementations and I cannot seem to figure it out.

Answer 1

First: your method DblLinkedBag::clear has a error, nodeToDelete never change (just deletes first node)
bool DblLinkedBag::remove(string item)
{
node* curPtr=start;
while (curPtr!=NULL)
{
if(item==curPtr->data)
{
if(curPtr->prev) curPtr->prev->next = curPtr->next;
if(curPtr->next) curPtr->next->prev = curPtr->prev;
delete curPtr;
itemCount--;
return true;
}
else
{
curPtr=curPtr->next;
}
}
return false;
}
What do you expect getFrequency() to do?