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LinkedList Search

unsensible (78)
I'm doing an assignment that requires various actions to be done on a linked list. AppendNode, InsertNode, DeleteNode, displayList, and a search list function. I was able to get all of these to work fine except for the search list function. My whole program exploded when I tried and when I comment out the search function it runs fine again.

Any help with this would be greatly appreciated.

Linked.h
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#ifndef LINKED_H
#define LINKED_H
#include<iostream>

template <class T>
class Linked
{
private:
  // Declare a structure for the list
 struct ListNode
 {
 T value; // The value in this node
 struct ListNode *next; // To point to the next node
 }; 
 
 ListNode *head; // List head pointer
 public:
 // Constructor
Linked()
 { head = NULL; }
 
 // Destructor
~Linked();
 

 // Linked list operations
 void appendNode(T);
 void insertNode(T);
 void deleteNode(T);
 void destroyList();
 void displayList() const;
 ListNode<T>* sequentialSearch(const T) const;
 };


template<class T>
Linked<T>::~Linked()
{
ListNode *nodePtr; // To traverse the list
ListNode *nextNode; // To point to the next node
 
 // Position nodePtr at the head of the list.
 nodePtr = head;
 
 // While nodePtr is not at the end of the list...
 while (nodePtr != NULL)
 {
 // Save a pointer to the next node.
 nextNode = nodePtr->next;
 
 // Delete the current node.
 delete nodePtr;
 
 // Position nodePtr at the next node.
 nodePtr = nextNode;
}
}


//insertnode
template <class T>
void Linked<T>::insertNode(T num)
  {
  ListNode *newNode; // A new node
  ListNode *nodePtr; // To traverse the list
  ListNode *previousNode = NULL; // The previous node
  
  // Allocate a new node and store num there.
  newNode = new ListNode;
  newNode->value = num;
  
  // If there are no nodes in the list
  // make newNode the first node
  if (!head)
  {
  head = newNode;
  newNode->next = NULL;
  }
  else // Otherwise, insert newNode
  {
  // Position nodePtr at the head of list.
  nodePtr = head;
  
  // Initialize previousNode to NULL.
  previousNode = NULL;
  
  // Skip all nodes whose value is less than num.
  while (nodePtr != NULL && nodePtr->value < num)
  { 
  previousNode = nodePtr;
  nodePtr = nodePtr->next;
  }
 
 // If the new node is to be the 1st in the list,
 // insert it before all other nodes.
 if (previousNode == NULL)
 {
	 head = newNode;
 newNode->next = nodePtr;
 }
 else // Otherwise insert after the previous node.
 {
 previousNode->next = newNode;
 newNode->next = nodePtr;
 }
 }
 }


//deletenode
template <class T>
void Linked<T>::deleteNode(T num)
 {
 ListNode *nodePtr; // To traverse the list
 ListNode *previousNode; // To point to the previous node 
// If the list is empty, do nothing.
 if (!head)
return;
// Determine if the first node is the one.
if (head->value == num)
 {
 nodePtr = head->next;
 delete head;
 head = nodePtr;
 }
 else
 {
 // Initialize nodePtr to head of list
 nodePtr = head;
 
 // Skip all nodes whose value member is 
 // not equal to num.
 while (nodePtr != NULL && nodePtr->value != num)
 { 
 previousNode = nodePtr;
 nodePtr = nodePtr->next;
}
 // If nodePtr is not at the end of the list, 
// link the previous node to the node after
// nodePtr, then delete nodePtr.
if (nodePtr)
{
previousNode->next = nodePtr->next;
delete nodePtr;
}
}
}

template <class T>
void Linked<T>::appendNode(T num)
  {
  ListNode *newNode; // To point to a new node
  ListNode *nodePtr; // To move through the list
  
  // Allocate a new node and store num there.
  newNode = new ListNode;
  newNode->value = num;
  newNode->next = NULL;
  
  // If there are no nodes in the list
  // make newNode the first node.
  if (!head)
  head = newNode;
  else // Otherwise, insert newNode at end.
  {
  // Initialize nodePtr to head of list.
  nodePtr = head;
  
  // Find the last node in the list.
  while (nodePtr->next)
  nodePtr = nodePtr->next;
  
  // Insert newNode as the last node.
  nodePtr->next = newNode;
  }
  }

template <class T>
void Linked<T>::displayList() const
  {
  ListNode *nodePtr; // To move through the list
  
  // Position nodePtr at the head of the list.
  nodePtr = head;
  
  // While nodePtr points to a node, traverse
  // the list.
  while (nodePtr)
  {
  // Display the value in this node.
  cout << nodePtr->value << endl;
  
  // Move to the next node.
  nodePtr = nodePtr->next;
  }
}

template <class T>
ListNode<T>* Linked<T>::sequentialSearch(const T& searchItem) const
   {
   LNode<T>* current;

   for (current = first; current != NULL && searchItem > current->data; current = current->next)
      ;

   if (current != NULL && searchItem == current->data)
      return current;
   else
      return NULL;
   }
 #endif 


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#include<iostream>
#include "Linked.h"

using namespace std;

int main(){

	Linked<double> list;
	cout<<"List is populated with 3 values: "<<endl<<endl;
	list.appendNode(2.5);
	list.appendNode(7.9);
	list.appendNode(12.6);
	list.displayList();
	cout<<endl;

	cout<<"10.5 is inserted into the list: "<<endl<<endl;
	list.insertNode(10.5);
	list.displayList();
	cout<<endl;

	cout<<"7.9 is deleted from the list: "<<endl<<endl;
	list.deleteNode(7.9);

	list.displayList();

	list.sequentialSearch(12.6);

	
	system("pause");
	return 0;

}
ne555 (10692)
http://www.cplusplus.com/forum/general/112111/
foo.cpp:32:2: error: ‘Linked<T>::ListNode’ is not a template
foo.cpp: In member function ‘void Linked<T>::displayList() const’:
foo.cpp:191:3: error: ‘cout’ was not declared in this scope
foo.cpp:191:29: error: ‘endl’ was not declared in this scope
foo.cpp: At global scope:
foo.cpp:199:1: error: ‘ListNode’ does not name a type
unsensible (78)
Hello Ne555, thank you for your response.

At this point I know where the error lies. I don't necessarily need to use the debugger to figure that out. For example, the following code runs fine:

Linked.h
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#ifndef LINKED_H
#define LINKED_H
#include<iostream>

template <class T>
class Linked
{
private:
  // Declare a structure for the list
 struct ListNode
 {
 T value; // The value in this node
 struct ListNode *next; // To point to the next node
 }; 
 
 ListNode *head; // List head pointer
 public:
 // Constructor
Linked()
 { head = NULL; }
 
 // Destructor
~Linked();
 

 // Linked list operations
 void appendNode(T);
 void insertNode(T);
 void deleteNode(T);
 void destroyList();
 void displayList() const;
 ///ListNode<T>* sequentialSearch(const T) const;
 };


template<class T>
Linked<T>::~Linked()
{
ListNode *nodePtr; // To traverse the list
ListNode *nextNode; // To point to the next node
 
 // Position nodePtr at the head of the list.
 nodePtr = head;
 
 // While nodePtr is not at the end of the list...
 while (nodePtr != NULL)
 {
 // Save a pointer to the next node.
 nextNode = nodePtr->next;
 
 // Delete the current node.
 delete nodePtr;
 
 // Position nodePtr at the next node.
 nodePtr = nextNode;
}
}


//insertnode
template <class T>
void Linked<T>::insertNode(T num)
  {
  ListNode *newNode; // A new node
  ListNode *nodePtr; // To traverse the list
  ListNode *previousNode = NULL; // The previous node
  
  // Allocate a new node and store num there.
  newNode = new ListNode;
  newNode->value = num;
  
  // If there are no nodes in the list
  // make newNode the first node
  if (!head)
  {
  head = newNode;
  newNode->next = NULL;
  }
  else // Otherwise, insert newNode
  {
  // Position nodePtr at the head of list.
  nodePtr = head;
  
  // Initialize previousNode to NULL.
  previousNode = NULL;
  
  // Skip all nodes whose value is less than num.
  while (nodePtr != NULL && nodePtr->value < num)
  { 
  previousNode = nodePtr;
  nodePtr = nodePtr->next;
  }
 
 // If the new node is to be the 1st in the list,
 // insert it before all other nodes.
 if (previousNode == NULL)
 {
	 head = newNode;
 newNode->next = nodePtr;
 }
 else // Otherwise insert after the previous node.
 {
 previousNode->next = newNode;
 newNode->next = nodePtr;
 }
 }
 }


//deletenode
template <class T>
void Linked<T>::deleteNode(T num)
 {
 ListNode *nodePtr; // To traverse the list
 ListNode *previousNode; // To point to the previous node 
// If the list is empty, do nothing.
 if (!head)
return;
// Determine if the first node is the one.
if (head->value == num)
 {
 nodePtr = head->next;
 delete head;
 head = nodePtr;
 }
 else
 {
 // Initialize nodePtr to head of list
 nodePtr = head;
 
 // Skip all nodes whose value member is 
 // not equal to num.
 while (nodePtr != NULL && nodePtr->value != num)
 { 
 previousNode = nodePtr;
 nodePtr = nodePtr->next;
}
 // If nodePtr is not at the end of the list, 
// link the previous node to the node after
// nodePtr, then delete nodePtr.
if (nodePtr)
{
previousNode->next = nodePtr->next;
delete nodePtr;
}
}
}

template <class T>
void Linked<T>::appendNode(T num)
  {
  ListNode *newNode; // To point to a new node
  ListNode *nodePtr; // To move through the list
  
  // Allocate a new node and store num there.
  newNode = new ListNode;
  newNode->value = num;
  newNode->next = NULL;
  
  // If there are no nodes in the list
  // make newNode the first node.
  if (!head)
  head = newNode;
  else // Otherwise, insert newNode at end.
  {
  // Initialize nodePtr to head of list.
  nodePtr = head;
  
  // Find the last node in the list.
  while (nodePtr->next)
  nodePtr = nodePtr->next;
  
  // Insert newNode as the last node.
  nodePtr->next = newNode;
  }
  }

template <class T>
void Linked<T>::displayList() const
  {
  ListNode *nodePtr; // To move through the list
  
  // Position nodePtr at the head of the list.
  nodePtr = head;
  
  // While nodePtr points to a node, traverse
  // the list.
  while (nodePtr)
  {
  // Display the value in this node.
  cout << nodePtr->value << endl;
  
  // Move to the next node.
  nodePtr = nodePtr->next;
  }
}
/*
template <class T>
ListNode<T>* Linked<T>::sequentialSearch(const T& searchItem) const
   {
   LNode<T>* current;

   for (current = first; current != NULL && searchItem > current->data; current = current->next)
      ;

   if (current != NULL && searchItem == current->data)
      return current;
   else
      return NULL;
   }
    */
 #endif


main.cpp
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#include<iostream>
#include "Linked.h"

using namespace std;

int main(){

	Linked<double> list;
	cout<<"List is populated with 3 values: "<<endl<<endl;
	list.appendNode(2.5);
	list.appendNode(7.9);
	list.appendNode(12.6);
	list.displayList();
	cout<<endl;

	cout<<"10.5 is inserted into the list: "<<endl<<endl;
	list.insertNode(10.5);
	list.displayList();
	cout<<endl;

	cout<<"7.9 is deleted from the list: "<<endl<<endl;
	list.deleteNode(7.9);

	list.displayList();

	//list.sequentialSearch(12.6);

	
	system("pause");
	return 0;

}


As you can see I commented out the sequentialSearch function header, definition, and call. The problem is that I just honestly cannot figure out for the life of me how to make a templated function that will search through a linked list for a specified value. I was able to get all the other functions working correctly and have attempted the search function.

Could anyone assist in helping me create this search function?

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