Question

my code has several functions; delete and backward functions are not working, rewrite the code for both functions and check them in the main:

#include<iostream>
#include<cassert>
using namespace std;

struct nodeType
{
   int info;
   nodeType *link;
};

class linkedList
{
public:

   void initializeList();

   bool isEmptyList();

   void print();

   int length();

   void destroyList();

   void insertFirst(int newItem);

   void insertLast(int newItem);

   int front();

   linkedList();

   void copyList(const linkedList otherList);

   void insertNewValue(int value);

   void deleteItem(int deleteItem);

   void Backward(int num);

private:

   int count;
   nodeType *first;
   nodeType *last;
};

int linkedList::front()
{
   assert(first != nullptr);
   return last->info;
}
bool linkedList::isEmptyList()
{
   return (first == nullptr);
}

void linkedList::insertFirst(int newItem)
{
   nodeType *newNode;

   newNode = new nodeType;

   newNode->info = newItem;
   newNode->link = first;
   first = newNode;

   count++;

   if (last == nullptr)
       last = newNode;
}

void linkedList::insertLast(int newItem)
{
   nodeType *newNode;

   newNode = new nodeType;
   newNode->info = newItem;
   newNode->link = nullptr;
   if (first == nullptr)
   {
       first = newNode;
       last = newNode;
       count++;
   }
   else
   {
       last->link = newNode;
       last = newNode;
       count++;
   }
}

linkedList::linkedList()
{
   first = nullptr;
   last = nullptr;
   count = 0;
}

void linkedList::destroyList()
{
   nodeType *temp;
   while (first != nullptr)
   {
       temp = first;
       first = first->link;
       delete temp;
   }
   last = nullptr;
   count = 0;
}

void linkedList::initializeList()
{
   destroyList();
}

void linkedList::print()
{
   nodeType *current;

   current = first;
   while (current != nullptr)
   {
       cout << current->info << " ";
       current = current->link;
   }
}

int linkedList::length()
{
   return count;
}

void linkedList::insertNewValue(int value)
{
   nodeType *curr = first; // set curr to first node of the list
   bool found = false; // set found to false
                       // loop over the list
   while (curr != nullptr)
   {
       if (curr->info == value) // value found, set found to true and exit the loop
       {
           found = true;
           break;
       }

       curr = curr->link;
   }

   if (!found) // value not found in list, insert value at end
       insertLast(value);
   else // value found in list, hence not inserted
       cout << "ERROR: " << value << " already inserted in the list. " << endl;

}

void linkedList::deleteItem(int deleteItem)
{
   nodeType *p, *q;
   q = nullptr;
   p = first;
   while (p != nullptr)
   {
       // p->info as we are accessing data and not the pointer
       if (p->info == deleteItem)
       {
           q = p;
           p->link = p->link->link;
           delete q;
           return;
       }
       p = p->link;
   }
}

void linkedList::copyList(const linkedList otherList)
{
   nodeType *newNode, *current, *fin;
   if (first != nullptr)
       initializeList();
   if (otherList.first == nullptr)
       first = nullptr;
   else
   {

       current = otherList.first;
       first = new nodeType;
       first->info = current->info;
       first->link = nullptr;
       last = first;
       current = current->link;

       while (current != nullptr)
       {
           // cout<<"here\n";
           nodeType *p = new nodeType();
           count++;
           p->info = current->info;
           p->link = nullptr;
           last->link = p;
           last = last->link;
           current = current->link;
       }
   }
   return;

}

void linkedList::Backward(int num)
{

   // Code changes
   // Addind node to the tail
   nodeType *p = new nodeType();
   count++;
   p->info = num;
   p->link = nullptr;
   if (first == nullptr)
   {
       first = last = p;
       return;
   }
   last->link = p;
   last = last->link;

}

int main()
{

   linkedList List;
   linkedList listForward;
   int num = -1, x;

   cout << "Enter numbers ending with -999" << endl;
   cin >> num;

   while (num != -999)
   {
       List.Backward(num);
       listForward.insertFirst(num);

       cin >> num;
   }
   cout << endl;

   cout << "The list in backward" << endl;
   List.print();

   cout << endl;
   cout << "The list in forward" << endl;
   listForward.print();

   cout << endl;

   cout << "Length of the list: " << List.length() << endl;

   cout << "Enter a number to add in the list " << endl;
   cin >> x;
   List.insertNewValue(x);
   cout << "The list after adding the number " << endl;
   List.print();
   cout << endl;

   cout << "The length of the list after adding a number is " << List.length() << endl;

   int el;
   cout << "Enter the value to be deleted in the list: " << endl;
   cin >> el;
   List.deleteItem(el);

   List.print();
   cout << endl;

   cout << "Enter new value to be added in the list: " << endl;
   int k;
   cin >> k;
   List.insertNewValue(k);

   List.print();
   cout << endl;

   cout << endl;
   cout << endl << "Creating a copy of the linked list" << endl;
   linkedList newList;
   newList.copyList(List);
   cout << "Printing the new linked list\n";
   newList.print();

   List.destroyList();
   cout << endl;
   cout << "After destroying the list, the length is " << List.length() << endl;

   system("pause");
   return 0;
}

Answer 1

void linkedList::deleteItem(int deleteItem)
{

   nodeType *p, *q;
   q = nullptr;
   p = first;

if (p==nullptr)

{

cout<<"linked list not initialized";

return ;

}
   while (p != nullptr)
   {
       // p->info as we are accessing data and not the pointer
       if (p->info == deleteItem)
       {
           q = p;
           p->link = p->link->link;
           delete q;
           return;
       }
       p = p->link;
   }