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linked list question

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Join Date: Jun 2008

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JackDurden JackDurden is offline

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linked list question

Oct 5th, 2008

Im having real trouble seeing this, how do I delete something out of a linked list if it is already there? My current delete function just deletes everything out of the list.

the text file contains numbers like this:
75
85
95
25
35
75
85
95
25

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <iostream>
#include <fstream>
 
using namespace std;
 
class List
{
public:
	void Insert(int);
	void Print();
	//
	void Delete(int);
	int Length(int);
};
 
struct node
{
	int item;
	node *nxt;
}; 
node *start_ptr = 0;
node *current;
 
 
void List::Delete(int item)
{
	if(start_ptr==NULL)
		cout<<"NULL";
 
	node* temp=start_ptr;
 
	if(temp->item==item)
	{
		start_ptr=temp->nxt;
 
		delete temp;
	}
}
void List::Insert(int item)
  {  
	  node *temp, *temp2;   // Temporary pointers
 
     // Reserve space for new node and fill it with data
     temp = new node; 
	 temp->item=item;
 
     temp->nxt = NULL;
 
     // Set up link to this node
     if (start_ptr == NULL)
       { 
		   start_ptr = temp;
		   current = start_ptr;
       }
     else
       { 
		   temp2 = start_ptr;
 
         while (temp2->nxt != NULL)
           {  
			   temp2 = temp2->nxt;
              // Move to next link in chain
           }
         temp2->nxt = temp;
       }
  }
void List::Print()
  {  
	 node *temp;
     temp = start_ptr;
 
     if (temp == NULL)
       cout << "The list is empty" << endl;
     else
       { while (temp != NULL)
	   {  // Display details for what temp points to
              cout  << temp->item << " ";
 
	      if (temp == current)
		cout << " <--";
              cout << endl;
	      temp = temp->nxt;
 
	   }
	 cout << "End of list" << endl;
       }
  }
int List::Length(int item)
{
	node *temp;
	temp=start_ptr;
	temp->item=item;
 
   int count=0;
 
   while(temp != 0)
   {
	   temp=temp->nxt;
	   count++;
   }
   return count;
}
void main()
  {  
	  List display;
	  fstream inFile;
	  node number;
	  inFile.open("numbers.txt");
 
while(inFile>>number.item)
{
	display.Insert(number.item);
	display.Delete(number.item);
}
	display.Print();
	//cout<<display.Length(number.item);
}
#include <iostream>
#include <fstream>

using namespace std;

class List
{
public:
	void Insert(int);
	void Print();
	//
	void Delete(int);
	int Length(int);
};

struct node
{
	int item;
	node *nxt;
}; 
node *start_ptr = 0;
node *current;


void List::Delete(int item)
{
	if(start_ptr==NULL)
		cout<<"NULL";

	node* temp=start_ptr;

	if(temp->item==item)
	{
		start_ptr=temp->nxt;

		delete temp;
	}
}
void List::Insert(int item)
  {  
	  node *temp, *temp2;   // Temporary pointers

     // Reserve space for new node and fill it with data
     temp = new node; 
	 temp->item=item;
    
     temp->nxt = NULL;

     // Set up link to this node
     if (start_ptr == NULL)
       { 
		   start_ptr = temp;
		   current = start_ptr;
       }
     else
       { 
		   temp2 = start_ptr;
       
         while (temp2->nxt != NULL)
           {  
			   temp2 = temp2->nxt;
              // Move to next link in chain
           }
         temp2->nxt = temp;
       }
  }
void List::Print()
  {  
	 node *temp;
     temp = start_ptr;
     
     if (temp == NULL)
       cout << "The list is empty" << endl;
     else
       { while (temp != NULL)
	   {  // Display details for what temp points to
              cout  << temp->item << " ";
	   
	      if (temp == current)
		cout << " <--";
              cout << endl;
	      temp = temp->nxt;

	   }
	 cout << "End of list" << endl;
       }
  }
int List::Length(int item)
{
	node *temp;
	temp=start_ptr;
	temp->item=item;
   
   int count=0;

   while(temp != 0)
   {
	   temp=temp->nxt;
	   count++;
   }
   return count;
}
void main()
  {  
	  List display;
	  fstream inFile;
	  node number;
	  inFile.open("numbers.txt");

while(inFile>>number.item)
{
	display.Insert(number.item);
	display.Delete(number.item);
}
	display.Print();
	//cout<<display.Length(number.item);
}

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Join Date: Aug 2005

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Re: linked list question

Oct 5th, 2008

Its done something like this: Note: not compiled or tested.

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node* temp=start_ptr;
node* prev = NULL;
while( temp )
{
   if( temp->item == item) 
   {
          // delete this node
         if( prev == NULL)
         {
            // we are at the head of the linked list, for remove the head
            start_ptr = start_ptr->nxt;
         }
         else
         {
               // we're somewhere in the middle of the linked list
               prev->nxt = temp->nxt;
        }
        delete temp;
        break; // all done
   }
   prev = hold;
    hold = hold->next;
}
node* temp=start_ptr;
node* prev = NULL;
while( temp )
{
   if( temp->item == item) 
   {
          // delete this node
         if( prev == NULL)
         {
            // we are at the head of the linked list, for remove the head
            start_ptr = start_ptr->nxt;
         }
         else
         {
               // we're somewhere in the middle of the linked list
               prev->nxt = temp->nxt;
        }
        delete temp;
        break; // all done
   }
   prev = hold;
    hold = hold->next;
}

Last edited by Ancient Dragon; Oct 5th, 2008 at 7:49 pm.

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Join Date: Jun 2008

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Re: linked list question

Oct 5th, 2008

This just seems to do the samething, I get an empty list by the end.

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Join Date: Aug 2005

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Re: linked list question

Oct 5th, 2008

post new code.

Don't PM me with questions -- you might get a nasty PM in response. If you have a question then post it in one of the forums.

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Join Date: Jun 2008

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JackDurden JackDurden is offline

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Re: linked list question

Oct 5th, 2008

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <iostream>
#include <fstream>
 
using namespace std;
 
class List
{
public:
	void Insert(int);
	void Print();
	//
	void Delete(int);
	int Length(int);
};
 
struct node
{
	int item;
	node *nxt;
}; 
node *start_ptr = 0;
node *current;
 
 
void List::Delete(int item)
{
	node* temp=start_ptr;
    node* prev = NULL;
	node* hold;
 
while( temp )
{
   if( temp->item == item) 
   {
          // delete this node
         if( prev == NULL)
         {
            // we are at the head of the linked list, for remove the head
            start_ptr = start_ptr->nxt;
         }
         else
         {
               // we're somewhere in the middle of the linked list
             prev->nxt = temp->nxt;
        }
        delete temp;
        break; // all done
   }
    prev = hold;
    hold = hold->nxt;
}
}
void List::Insert(int item)
  {  
	  node *temp, *temp2;   // Temporary pointers
 
     // Reserve space for new node and fill it with data
     temp = new node; 
	 temp->item=item;
 
     temp->nxt = NULL;
 
     // Set up link to this node
     if (start_ptr == NULL)
       { 
		   start_ptr = temp;
		   current = start_ptr;
       }
     else
       { 
		   temp2 = start_ptr;
 
         while (temp2->nxt != NULL)
           {  
			   temp2 = temp2->nxt;
              // Move to next link in chain
           }
         temp2->nxt = temp;
       }
  }
void List::Print()
  {  
	 node *temp;
     temp = start_ptr;
 
     if (temp == NULL)
       cout << "The list is empty" << endl;
     else
       { while (temp != NULL)
	   {  // Display details for what temp points to
              cout  << temp->item << " ";
 
	      if (temp == current)
		cout << " <--";
              cout << endl;
	      temp = temp->nxt;
 
	   }
	 cout << "End of list" << endl;
       }
  }
int List::Length(int item)
{
	node *temp;
	temp=start_ptr;
	temp->item=item;
 
   int count=0;
 
   while(temp != 0)
   {
	   temp=temp->nxt;
	   count++;
   }
   return count;
}
void main()
  {  
	  List display;
	  fstream inFile;
	  node number;
	  inFile.open("numbers.txt");
 
while(inFile>>number.item)
{
	display.Insert(number.item);
	display.Delete(number.item);
}
 
	display.Print();
	//cout<<display.Length(number.item);
}
#include <iostream>
#include <fstream>

using namespace std;

class List
{
public:
	void Insert(int);
	void Print();
	//
	void Delete(int);
	int Length(int);
};

struct node
{
	int item;
	node *nxt;
}; 
node *start_ptr = 0;
node *current;


void List::Delete(int item)
{
	node* temp=start_ptr;
    node* prev = NULL;
	node* hold;

while( temp )
{
   if( temp->item == item) 
   {
          // delete this node
         if( prev == NULL)
         {
            // we are at the head of the linked list, for remove the head
            start_ptr = start_ptr->nxt;
         }
         else
         {
               // we're somewhere in the middle of the linked list
             prev->nxt = temp->nxt;
        }
        delete temp;
        break; // all done
   }
    prev = hold;
    hold = hold->nxt;
}
}
void List::Insert(int item)
  {  
	  node *temp, *temp2;   // Temporary pointers

     // Reserve space for new node and fill it with data
     temp = new node; 
	 temp->item=item;
    
     temp->nxt = NULL;

     // Set up link to this node
     if (start_ptr == NULL)
       { 
		   start_ptr = temp;
		   current = start_ptr;
       }
     else
       { 
		   temp2 = start_ptr;
       
         while (temp2->nxt != NULL)
           {  
			   temp2 = temp2->nxt;
              // Move to next link in chain
           }
         temp2->nxt = temp;
       }
  }
void List::Print()
  {  
	 node *temp;
     temp = start_ptr;
     
     if (temp == NULL)
       cout << "The list is empty" << endl;
     else
       { while (temp != NULL)
	   {  // Display details for what temp points to
              cout  << temp->item << " ";
	   
	      if (temp == current)
		cout << " <--";
              cout << endl;
	      temp = temp->nxt;

	   }
	 cout << "End of list" << endl;
       }
  }
int List::Length(int item)
{
	node *temp;
	temp=start_ptr;
	temp->item=item;
   
   int count=0;

   while(temp != 0)
   {
	   temp=temp->nxt;
	   count++;
   }
   return count;
}
void main()
  {  
	  List display;
	  fstream inFile;
	  node number;
	  inFile.open("numbers.txt");

while(inFile>>number.item)
{
	display.Insert(number.item);
	display.Delete(number.item);
}
	
	display.Print();
	//cout<<display.Length(number.item);
}

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Join Date: Aug 2005

Posts: 15,597

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Ancient Dragon Ancient Dragon is offline

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Re: linked list question

Oct 5th, 2008

The problem is in main(), not that delete function. First it calls insert to insert a new number then turns right around and deletes it. Delete that line

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
while(inFile>>number.item)
{
	display.Insert(number.item);
	//display.Delete(number.item);  <<<<< delete this line
}
while(inFile>>number.item)
{
	display.Insert(number.item);
	//display.Delete(number.item);  <<<<< delete this line
}

Last edited by Ancient Dragon; Oct 5th, 2008 at 9:07 pm.

Don't PM me with questions -- you might get a nasty PM in response. If you have a question then post it in one of the forums.

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Join Date: Jun 2008

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JackDurden JackDurden is offline

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Re: linked list question

Oct 5th, 2008

But I want the delete function to delete any duplicates in the linked list. If I just delete that function then I still have the whole Linked list, duplicates included.
the text file contains numbers like this:
75
85
95
25
35
75
85
95
25

I want it to display these numbers only out of that list:
75
85
95
25
35

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Join Date: Aug 2005

Posts: 15,597

Reputation: Ancient Dragon has a reputation beyond repute

Solved Threads: 1489

Ancient Dragon Ancient Dragon is offline

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Still Learning

Re: linked list question

Oct 5th, 2008

Check to see if the number is already in the list before adding it. The delete() function is not the place to do that. Write another class method that does nothing but search the list for a number, return true if the number already exists in the list or false if it doesn't. Then if it doesn't call that Insert() function.

Last edited by Ancient Dragon; Oct 5th, 2008 at 9:23 pm.

Don't PM me with questions -- you might get a nasty PM in response. If you have a question then post it in one of the forums.