Unordered Linked List (C++) - c++

Question

I'm trying to learn Linked List, but I encountered a problem.
below is the code for linkedlist.h file
#ifndef H_LinkedListType
#define H_LinkedListType
#include <iostream>
#include <cassert>
using namespace std;
//Definition of the node
template <class Type>
struct nodeType
{
Type info;
nodeType<Type> *link;
};
template <class Type>
class linkedListIterator
{
public:
linkedListIterator();
//Default constructor
//Postcondition: current = nullptr;
linkedListIterator(nodeType<Type> *ptr);
//Constructor with a parameter.
//Postcondition: current = ptr;
Type operator*();
//Function to overload the dereferencing operator *.
//Postcondition: Returns the info contained in the node.
linkedListIterator<Type> operator++();
//Overload the pre-increment operator.
//Postcondition: The iterator is advanced to the next
// node.
bool operator==(const linkedListIterator<Type>& right) const;
//Overload the equality operator.
//Postcondition: Returns true if this iterator is equal to
// the iterator specified by right,
// otherwise it returns the value false.
bool operator!=(const linkedListIterator<Type>& right) const;
//Overload the not equal to operator.
//Postcondition: Returns true if this iterator is not
// equal to the iterator specified by
// right; otherwise it returns the value
// false.
private:
nodeType<Type> *current; //pointer to point to the current
//node in the linked list
};
template <class Type>
linkedListIterator<Type>::linkedListIterator()
{
current = nullptr;
}
template <class Type>
linkedListIterator<Type>::
linkedListIterator(nodeType<Type> *ptr)
{
current = ptr;
}
template <class Type>
Type linkedListIterator<Type>::operator*()
{
return current->info;
}
template <class Type>
linkedListIterator<Type> linkedListIterator<Type>::
operator++()
{
current = current->link;
return *this;
}
template <class Type>
bool linkedListIterator<Type>::operator==
(const linkedListIterator<Type>& right) const
{
return (current == right.current);
}
template <class Type>
bool linkedListIterator<Type>::operator!=
(const linkedListIterator<Type>& right) const
{ return (current != right.current);
}
//***************** class linkedListType ****************
template <class Type>
class linkedListType
{
public:
const linkedListType<Type>& operator=
(const linkedListType<Type>&);
//Overload the assignment operator.
void initializeList();
//Initialize the list to an empty state.
//Postcondition: first = nullptr, last = nullptr,
// count = 0;
bool isEmptyList() const;
//Function to determine whether the list is empty.
//Postcondition: Returns true if the list is empty,
// otherwise it returns false.
void print() const;
//Function to output the data contained in each node.
//Postcondition: none
int length() const;
//Function to return the number of nodes in the list.
//Postcondition: The value of count is returned.
void destroyList();
//Function to delete all the nodes from the list.
//Postcondition: first = nullptr, last = nullptr,
// count = 0;
Type front() const;
//Function to return the first element of the list.
//Precondition: The list must exist and must not be
// empty.
//Postcondition: If the list is empty, the program
// terminates; otherwise, the first
// element of the list is returned.
Type back() const;
//Function to return the last element of the list.
//Precondition: The list must exist and must not be
// empty.
//Postcondition: If the list is empty, the program
// terminates; otherwise, the last
// element of the list is returned.
virtual bool search(const Type& searchItem) const = 0;
//Function to determine whether searchItem is in the list.
//Postcondition: Returns true if searchItem is in the
// list, otherwise the value false is
// returned.
virtual void insertFirst(const Type& newItem) = 0;
//Function to insert newItem at the beginning of the list.
//Postcondition: first points to the new list, newItem is
// inserted at the beginning of the list,
// last points to the last node in the list,
// and count is incremented by 1.
virtual void insertLast(const Type& newItem) = 0;
//Function to insert newItem at the end of the list.
//Postcondition: first points to the new list, newItem
// is inserted at the end of the list,
// last points to the last node in the
// list, and count is incremented by 1.
virtual void deleteNode(const Type& deleteItem) = 0;
//Function to delete deleteItem from the list.
//Postcondition: If found, the node containing
// deleteItem is deleted from the list.
// first points to the first node, last
// points to the last node of the updated
// list, and count is decremented by 1.
linkedListIterator<Type> begin();
//Function to return an iterator at the begining of
//the linked list.
//Postcondition: Returns an iterator such that current
// is set to first.
linkedListIterator<Type> end();
//Function to return an iterator one element past the
//last element of the linked list.
//Postcondition: Returns an iterator such that current
// is set to nullptr.
linkedListType();
//Default constructor
//Initializes the list to an empty state.
//Postcondition: first = nullptr, last = nullptr,
// count = 0;
linkedListType(const linkedListType<Type>& otherList);
//copy constructor
~linkedListType();
//Destructor
//Deletes all the nodes from the list.
//Postcondition: The list object is destroyed.
protected:
int count; //variable to store the number of
//elements in the list
nodeType<Type> *first; //pointer to the first node of the list
nodeType<Type> *last; //pointer to the last node of the list
private:
void copyList(const linkedListType<Type>& otherList);
//Function to make a copy of otherList.
//Postcondition: A copy of otherList is created and
// assigned to this list.
};
template <class Type>
bool linkedListType<Type>::isEmptyList() const
{
return (first == nullptr);
}
template <class Type>
linkedListType<Type>::linkedListType() //default constructor
{
first = nullptr;
last = nullptr;
count = 0;
}
template <class Type>
void linkedListType<Type>::destroyList()
{
nodeType<Type> *temp; //pointer to deallocate the memory
//occupied by the node
while (first != nullptr) //while there are nodes in
{ //the list
temp = first; //set temp to the current node
first = first->link; //advance first to the next node
delete temp; //deallocate the memory occupied by temp
}
last = nullptr; //initialize last to nullptr; first has
//already been set to nullptr by the while loop
count = 0;
}
template <class Type>
void linkedListType<Type>::initializeList()
{
destroyList(); //if the list has any nodes, delete them
}
template <class Type>
void linkedListType<Type>::print() const
{
nodeType<Type> *current; //pointer to traverse the list
current = first; //set current so that it points to
//the first node
while (current != nullptr) //while more data to print
{
cout << current->info << " ";
current = current->link;
}
}//end print
template <class Type>
int linkedListType<Type>::length() const
{
return count;
} //end length
template <class Type>
Type linkedListType<Type>::front() const
{
assert(first != nullptr);
return first->info; //return the info of the first node
}//end front
template <class Type>
Type linkedListType<Type>::back() const
{
assert(last != nullptr);
return last->info; //return the info of the last node
}//end back
template <class Type>
linkedListIterator<Type> linkedListType<Type>::begin()
{
linkedListIterator<Type> temp(first);
return temp;
}
template <class Type>
linkedListIterator<Type> linkedListType<Type>::end()
{
linkedListIterator<Type> temp(nullptr);
return temp;
}
template <class Type>
void linkedListType<Type>::copyList
(const linkedListType<Type>& otherList)
{
nodeType<Type> *newNode; //pointer to create a node
nodeType<Type> *current; //pointer to traverse the list
if (first != nullptr) //if the list is nonempty, make it empty
destroyList();
if (otherList.first == nullptr) //otherList is empty
{
first = nullptr;
last = nullptr;
count = 0;
}
else
{
current = otherList.first; //current points to the
//list to be copied
count = otherList.count;
//copy the first node
first = new nodeType<Type>; //create the node
first->info = current->info; //copy the info
first->link = nullptr; //set the link field of
//the node to nullptr
last = first; //make last point to the
//first node
current = current->link; //make current point to
//the next node
//copy the remaining list
while (current != nullptr)
{
newNode = new nodeType<Type>; //create a node
newNode->info = current->info; //copy the info
newNode->link = nullptr; //set the link of
//newNode to nullptr
last->link = newNode; //attach newNode after last
last = newNode; //make last point to
//the actual last node
current = current->link; //make current point
//to the next node
}//end while
}//end else
}//end copyList
template <class Type>
linkedListType<Type>::~linkedListType() //destructor
{
destroyList();
}//end destructor
template <class Type>
linkedListType<Type>::linkedListType
(const linkedListType<Type>& otherList)
{
first = nullptr;
copyList(otherList);
}//end copy constructor
//overload the assignment operator
template <class Type>
const linkedListType<Type>& linkedListType<Type>::operator=
(const linkedListType<Type>& otherList)
{
if (this != &otherList) //avoid self-copy
{
copyList(otherList);
}//end else
return *this;
}
#endif
Below is the code for the testProgLinkedList.cpp
//This program tests various operation of a linked list
//34 62 21 90 66 53 88 24 10 -999
#include <iostream> //Line 1
#include "unorderedLinkedList.h" //Line 2
using namespace std; //Line 3
int main() //Line 4
{ //Line 5
unorderedLinkedList<int> list1, list2; //Line 6
int num; //Line 7
cout << "Line 8: Enter integers ending "
<< "with -999" << endl; //Line 8
cin >> num; //Line 9
while (num != -999) //Line 10
{ //Line 11
list1.insertLast(num); //Line 12
cin >> num; //Line 13
} //Line 14
cout << endl; //Line 15
cout << "Line 16: list1: "; //Line 16
list1.print(); //Line 17
cout << endl; //Line 18
cout << "Line 19: Length of list1: "
<< list1.length() << endl; //Line 19
list2 = list1; //test the assignment operator Line 20
cout << "Line 21: list2: "; //Line 21
list2.print(); //Line 22
cout << endl; //Line 23
cout << "Line 24: Length of list2: "
<< list2.length() << endl; //Line 24
cout << "Line 25: Enter the number to be "
<< "deleted: "; //Line 25
cin >> num; //Line 26
cout << endl; //Line 27
list2.deleteNode(num); //Line 28
cout << "Line 29: After deleting " << num
<< " list2: " << endl; //Line 29
list2.print(); //Line 30
cout << endl; //Line 31
cout << "Line 32: Length of list2: "
<< list2.length() << endl; //Line 32
cout << endl << "Line 33: Output list1 "
<< "using an iterator" << endl; //Line 33
linkedListIterator<int> it; //Line 34
for (it = list1.begin(); it != list1.end();
++it) //Line 35
cout << *it << " "; //Line 36
cout << endl; //Line 37
return 0; //Line 38
} //Line 39
Below is the code for the unorderedLinkList.h file
#ifndef H_UnorderedLinkedList
#define H_UnorderedLinkedList
#include "linkedList.h"
using namespace std;
template <class Type>
class unorderedLinkedList: public linkedListType<Type>
{
public:
bool search(const Type& searchItem) const;
//Function to determine whether searchItem is in the list.
//Postcondition: Returns true if searchItem is in the
// list, otherwise the value false is
// returned.
void insertFirst(const Type& newItem);
//Function to insert newItem at the beginning of the list.
//Postcondition: first points to the new list, newItem is
// inserted at the beginning of the list,
// last points to the last node in the
// list, and count is incremented by 1.
void insertLast(const Type& newItem);
//Function to insert newItem at the end of the list.
//Postcondition: first points to the new list, newItem
// is inserted at the end of the list,
// last points to the last node in the
// list, and count is incremented by 1.
void deleteNode(const Type& deleteItem);
//Function to delete deleteItem from the list.
//Postcondition: If found, the node containing
// deleteItem is deleted from the list.
// first points to the first node, last
// points to the last node of the updated
// list, and count is decremented by 1.
};
template <class Type>
bool unorderedLinkedList<Type>::
search(const Type& searchItem) const
{
nodeType<Type> *current; //pointer to traverse the list
bool found = false;
current = first; //set current to point to the first
//node in the list
while (current != nullptr && !found) //search the list
if (current->info == searchItem) //searchItem is found
found = true;
else
current = current->link; //make current point to
//the next node
return found;
}//end search
template <class Type>
void unorderedLinkedList<Type>::insertFirst(const Type& newItem)
{
nodeType<Type> *newNode; //pointer to create the new node
newNode = new nodeType<Type>; //create the new node
newNode->info = newItem; //store the new item in the node
newNode->link = first; //insert newNode before first
first = newNode; //make first point to the
//actual first node
count++; //increment count
if (last == nullptr) //if the list was empty, newNode is also
//the last node in the list
last = newNode;
}//end insertFirst
template <class Type>
void unorderedLinkedList<Type>::insertLast(const Type& newItem)
{
nodeType<Type> *newNode; //pointer to create the new node
newNode = new nodeType<Type>; //create the new node
newNode->info = newItem; //store the new item in the node
newNode->link = nullptr; //set the link field of newNode
//to nullptr
if (first == nullptr) //if the list is empty, newNode is
//both the first and last node
{
first = newNode;
last = newNode;
count++; //increment count
}
else //the list is not empty, insert newNode after last
{
last->link = newNode; //insert newNode after last
last = newNode; //make last point to the actual
//last node in the list
count++; //increment count
}
}//end insertLast
template <class Type>
void unorderedLinkedList<Type>::deleteNode(const Type& deleteItem)
{
nodeType<Type> *current; //pointer to traverse the list
nodeType<Type> *trailCurrent; //pointer just before current
bool found;
if (first == nullptr) //Case 1; the list is empty.
cout << "Cannot delete from an empty list."
<< endl;
else
{
if (first->info == deleteItem) //Case 2
{
current = first;
first = first->link;
count--;
if (first == nullptr) //the list has only one node
last = nullptr;
delete current;
}
else //search the list for the node with the given info
{
found = false;
trailCurrent = first; //set trailCurrent to point
//to the first node
current = first->link; //set current to point to
//the second node
while (current != nullptr && !found)
{
if (current->info != deleteItem)
{
trailCurrent = current;
current = current-> link;
}
else
found = true;
}//end while
if (found) //Case 3; if found, delete the node
{
trailCurrent->link = current->link;
count--;
if (last == current) //node to be deleted
//was the last node
last = trailCurrent; //update the value
//of last
delete current; //delete the node from the list
}
else
cout << "The item to be deleted is not in "
<< "the list." << endl;
}//end else
}//end else
}//end deleteNode
#endif
But when I compiled the code it showed error messages as seen below:
I don't know how to fix the errors as I am new to coding. Please help me.
Error messages

Answer 1

Generally speaking you can ignore all the errors after the first couple. Fix errors one at a time starting with the first.
This line
current = first; //set current to point to the first
//node in the list
generates an error which says that the compiler doesn't know what first is. Now it looks like there is a declaration of first in linkedListType<Type> but the compiler doesn't find it. Why? Well that is complicated, but basically it is because your class is a template and the name is defined in a parent template class. Fortunately there is a simple fix, just add this->
current = this->first; //set current to point to the first
//node in the list
More details here, but be warned it's complicated.