Link List container class question

Hi Experts,

I am almost done with my assignment...but have a few issues:

1. When I modify a card using "ChangeCard" function....and enter a last name that doesn't exist....I get a "Segmentation fault" error ??? Can someone clarify and help me out here

2. The program works fine as long as I add a couple of records...and also delete all of them.
But once I try to re-add records after deleting all of the records.....and then try to display the re-added records...It says "NO RECORDS FOUND">>>Am I doing somethign wrong here??

Please help ??


#include <iostream>
#include <string>

using namespace std;

class RolodexCard {
 private:
   string firstname;
   string lastname;
   string occupation;
   string address;
   string phone_number;
   RolodexCard * next;

public:      
   RolodexCard(string,string,string,string,string);
   RolodexCard();
   void set_next(RolodexCard *);
   void set_fname(string);
   void set_lname(string);
   void set_occup(string);
   void set_addr(string);
   void set_phone(string);
   RolodexCard * get_next();
   string get_lname();
   bool operator > (RolodexCard& op1);
   void print_output();
};


RolodexCard::RolodexCard(string fname, string lname, string occup, string addr,
string phone_num)
{
      firstname = fname;
      lastname = lname;
      occupation = occup;
      address = addr;
      phone_number = phone_num;
      next = 0;
}

RolodexCard::RolodexCard()
{
        next = 0;  
}

void RolodexCard::set_next(RolodexCard* next_info)
{
    next = next_info;  
}

void RolodexCard::set_fname(string _fname)
{
    firstname = _fname;
}

void RolodexCard::set_lname(string _lname)
{
    lastname = _lname;
}

void RolodexCard::set_occup(string _occup)
{
    occupation = _occup;
}

void RolodexCard::set_addr(string _addr)  
{
    address = _addr;    
}

void RolodexCard::set_phone(string _phone)
{
    phone_number = _phone;
}


RolodexCard * RolodexCard::get_next()
{
      return next;
}

string RolodexCard::get_lname()
{
        return lastname;
}

bool RolodexCard::operator > (RolodexCard & op1)
{
      bool isGreat = false;

      if( lastname > op1.lastname )
            
            isGreat = true;

      return isGreat;
}

void RolodexCard::print_output()
{
    cout << "***********************************"<<endl;
    cout << "Firstname :" << " "  <<  firstname << endl;
    cout << "Lastname  :" << " "  << lastname << endl;
    cout << "Occupation:" << " "  << occupation << endl;
    cout << "Address   :" << " "  << address << endl;  
    cout << "Phone     :" << " "  << phone_number << endl;
 }


class RolodexFile
{
private:
   RolodexCard * head;
   RolodexCard * tail;
   RolodexCard * currptr;
public:
   void AddInOrder();
   void AddAtHead(RolodexCard *newCard);
   void AddAtTail(RolodexCard *newCard);
   void DeleteCard();
   void ChangeCard();
   void DisplayRolodex();
   void Erase();
   int handle_choice(int);
   RolodexFile(); // default CTOR
   ~RolodexFile();  // default DTOR
};



RolodexFile::RolodexFile()
{
      head = 0;
      tail = 0;
        currptr = head;
}

RolodexFile::~RolodexFile()
{
      Erase();
}

void RolodexFile::AddInOrder()  // This is Insertion Sort
{      
        string _fname;string _lname;string _occup; string _addr; string _phone;
        cout << "\nADDING A NEW CARD\n";
        cout << "Firstname: ";
        cin.ignore(80,'\n');
        getline(cin,_fname);
        cout << "Lastname: ";
        getline(cin,_lname);
        cout << "Occupation: ";
        getline(cin,_occup);
        cout << "Address: ";
        getline(cin,_addr);
        cout << "Phone number: ";
        getline(cin,_phone);
        RolodexCard * newCard = new RolodexCard(_fname,_lname,_occup,_addr,_phone);
        RolodexCard * nextptr = head;
      RolodexCard * lastptr = 0;

      while(nextptr!=0 && (*newCard) > (*nextptr))
      {
            lastptr = nextptr;
            nextptr = nextptr->get_next();
      }

      if (nextptr == 0)   // hit end of list, AddAtTail, so even if it didn't enter the loop, it should atleast add at the Tail
        {
            AddAtTail(newCard);
      }
      else
      {
            if (lastptr == 0)   // this means to add at the beginning
            {
                  AddAtHead(newCard);
            }

            else              // this means tp add at the middle
            {
                  newCard->set_next(nextptr);
                    lastptr->set_next(newCard);
            }
      }
      
}



void RolodexFile::AddAtTail(RolodexCard *newCard)
{
    if (tail == 0)
      head = newCard;
    else
      tail->set_next(newCard);

    tail=newCard;
}


void RolodexFile::AddAtHead(RolodexCard *newCard)
{
      if (head==0)
            tail = newCard;

      newCard->set_next(head);
      head = newCard;
}


void RolodexFile::DeleteCard()
{
 string _lname; int i = 0;
 RolodexCard * prevptr = 0; // initialize previous ptr to NULL
 cout << "\nEnter the Lastname of the card that you want to delete: ";
 cin.ignore(80,'\n');
 getline(cin,_lname);
 for(currptr = head; currptr != 0; currptr= currptr->get_next() )
 {
   if (currptr->get_lname() == _lname)
   {
     if (prevptr == 0)
        head = currptr->get_next();
     else
        prevptr->set_next(currptr->get_next());
     delete currptr;
     i = 1;
   }
   else
     prevptr = currptr;
 }
  if (i == 0)
 {
   cout << "\n\nNO MATCH FOUND FOR THE LASTNAME YOU ENTERED\n\n";
 }  
}


void RolodexFile::ChangeCard()
{
 string _fname;string _lname;string _occup;string _addr;string _phone;
 int choice; int flag = 0;
 RolodexCard * temp = head;
 cout << "\nEnter the lastname of the card you want to modify\n";
 cin.ignore(80,'\n');
 getline(cin,_lname);
 while((temp->get_lname() != _lname) && temp != 0)
 {
   temp = temp->get_next();
 }
 if (temp != 0)
 {
   flag = 1;
   cout << "\nCARD FOUND\n";
   cout << "\nChoose one of the following\n";
   cout << "0 - Change Firstname\n";
   cout << "1 - Change Lastname\n";
   cout << "2 - Change Occupation\n";
   cout << "3 - Change Address\n";
   cout << "4 - Change Phone number\n";
   cout << "\nENTER CHOICE: ";
   cin >> choice;
   switch(choice)
   {
    case 0:
          cout << "Enter the new Firstname: ";
          cin.ignore(80,'\n');
          getline(cin,_fname);
          temp->set_fname(_fname);
          break;
    case 1:
          cout << "Enter the new Lastname: ";
          cin.ignore(80,'\n');
          getline(cin,_lname);
          temp->set_lname(_lname);
          break;
    case 2:
          cout << "Enter the new Occupation: ";
          cin.ignore(80,'\n');
          getline(cin,_occup);
          temp->set_occup(_occup);
          break;
    case 3:
          cout << "Enter the new Address:   ";
          cin.ignore(80,'\n');
          getline(cin,_addr);
          temp->set_addr(_addr);
          break;
    case 4:
          cout << "Enter the new Phone Number: ";
          cin.ignore(80,'\n');
          getline(cin,_phone);
          temp->set_phone(_phone);
          break;
    default:
          cout << "\nInvalid choice\n";
          break;
    }
  }
  if (flag == 0)
  {
    cout << "\n\nNO MATCH FOUND FOR THE LASTNAME YOU ENTERED\n\n";
  }
}


void RolodexFile::Erase()
{
      RolodexCard * temp = head;
        currptr = head;

      while(currptr)
      {
        currptr = currptr->get_next();
          delete temp;
          temp = currptr;      
      }
}


void RolodexFile::DisplayRolodex()
{
    currptr = head;
    if(currptr != 0)
    {
       cout << "*************************************\n";
       cout << "** Displaying the Rolodex Cards ***\n";
       while (currptr)
       {
          currptr->print_output();
          currptr = currptr->get_next();
       }
    }
    else
    cout << "\n\nEVERYTHING Erased NO LIST to PRINT ******* ";
    currptr = head;
}

int RolodexFile::handle_choice(int choice)
{
    switch(choice)
    {
    case 0:
          return 0;
    case 1:
        AddInOrder();
        cout << "\n\nPress any key to continue....";
        getchar();
        return 1;
    case 2:
       DisplayRolodex();
       cout << "\n\nPress any key to continue....";
       getchar();
       return 1;
    case 3:
      ChangeCard();
      cout << "\n\nPress any key to continue....";
      getchar();
      return 1;
   case 4:
      DeleteCard();
      cout << "\n\nPress any key to continue...";
      getchar();
      return 1;
   default:  
     cout << "\n\nInvalid Choice !!";
     cout << "\n\nPress any key to continue....";
     getchar();
     return 0;
   }
}



void main()
{
  int choice; int flag=1;
  RolodexFile r_file;
  do
   {
     cout << "\nWELCOME - ROLODEX CARDS\n";
     cout << "*****************************\n";
     cout << "0 - Exit Program\n";
     cout << "1 - Add a Card (will be sorted in order)\n";
     cout << "2 - Display Rolodex\n";
     cout << "3 - Search Rolodex by Lastname and Change\n";
     cout << "4 - Delete a Card\n";
     cout << " Enter Choice: ";
     cin >> choice;
     flag = r_file.handle_choice(choice);
     system("clear");
   } while (flag != 0);