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

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?