Help with my linked list

**evildotaing** · 11-25-2011

Code:

#include <iostream>

using namespace std;

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

void main(void)
{
	nodeType * first, * last, *newNode, * current ,*previous;
	first = last = newNode = NULL;

	//int num;

	first = NULL;
	last = NULL;
	cout << "Building a linked list: " << endl;

	newNode = new nodeType;
	newNode -> info = 5;
	newNode -> link = NULL;
	cout << "My first node is " <<newNode -> info << endl;

	first = last = newNode;

	newNode = new nodeType;
	newNode -> info = 15;
	newNode -> link = NULL;
	cout << "My second node is " <<newNode -> info << endl;
	last->link = newNode;
	last = newNode;

	newNode = new nodeType;
	newNode -> info = 10;
	newNode -> link = NULL;
	cout << "My third node is " <<newNode -> info << endl;
	last->link = newNode;
	last = newNode;

	newNode = new nodeType;
	newNode -> info = 22;
	newNode -> link = NULL;
	cout << "My fourth node is " <<newNode -> info << endl;
	last->link = newNode;
	last = newNode;
	
	cout << "End of building a linked list: " << endl;


	cout << "Transvering " << endl;
	current = first;
	
	cout << "Transvering through the first node" << endl;
	cout << current-> info << endl;

	cout << "Transvering thorugh the second node" << endl;
	current = current->link ;
	cout << current -> info << endl;

	cout << "Transvering through the third node" << endl;
	current = current-> link;
	cout << current -> info << endl;

	cout << "Transvering through the fourth node" << endl;
	current = current-> link;
	cout << current -> info << endl;
	
	cout << "Transvering through the last node" << endl;
	if (current = last)
	{
		cout << "No transvering allowed: " << endl;
	}
	else
	{
		cout << current -> info << endl;
	}
	cout << endl;
	
	cout << "Transvering back to the first node: " << endl;
	current = first;
	cout << current -> info << endl;


	//Deleting third node
	cout << "Deleting third node from the link list" << endl;
	current = first;
	previous = first;
	previous ->link = previous ->link -> link;
	current = previous ->link;
	previous -> link = current->link;
	delete current;

	current = first;
	cout << current -> info << endl;
	current = current ->link->link;
	cout << current -> info << endl;
	current = current ->link->link->link;
	cout << current -> info << endl;
	
	system ("pause");
}

Is my linked above correct, i got problem deleting nodes , any1 got any idead how should I do it. Anyway I not sure if i miss anything on the linked list i forgot to add.Some1 help me. Thank you. I am trying to delete the third nodes.

**hk_mp5kpdw** · 11-25-2011

#1

Code:

void main(void)

It should always be int main not void main, people tend to get picky about this one here.

#2

Code:

newNode = new nodeType;
newNode -> info = 5;
newNode -> link = NULL;
....
newNode = new nodeType;
newNode -> info = 15;
newNode -> link = NULL;
...
newNode = new nodeType;
newNode -> info = 10;
newNode -> link = NULL;
...
newNode = new nodeType;
newNode -> info = 22;
newNode -> link = NULL;

Create a constructor for your nodeType struct to help out and reduce some of that code:

Code:

struct nodeType
{
    int info;
    nodeType * link;
    nodeType(int value) : info(value), link(NULL) {}
};

The above code then becomes:

Code:

newNode = new nodeType(5);
....
newNode = new nodeType(15);
...
newNode = new nodeType(10);
...
newNode = new nodeType(22);

#3

Code:

if (current = last)

Typo? It should be == not =

#4

Code:

//Deleting third node
cout << "Deleting third node from the link list" << endl;
current = first;
previous = first;
previous ->link = previous ->link -> link;
current = previous ->link;
previous -> link = current->link;
delete current;

The lines that unravel everything here are the ones in red above. For the first one, by repointing previous->link you are also affecting current->link and first->link since they are all the same node in your list. That one line destroys your list since you've lost any pointer you had to the second node in the list - the one that contains the number 15. For the second one, you then make first's link pointer point to the last node in the list before deleting the third node (current). The end result is that you end up with a list of two elements - 5 and 22.

If you want to delete the third node, then move previous, not previous->link:

Code:

previous = first->link;         // Previous points to 2nd node
current = previous->link;       // Current points to 3rd node
previous->link = current->link; // 2nd node's link pointer reset to skip to the 4th node
delete current;                 // Delete the third node

However, that said I would create functions to both insert a node at the end of the existing list and to delete a given node.

As a side note, certain operations, such as deletion of a node, are easier when your lists are doubly linked instead of singly linked. You are also manually managing your first/last pointers, this should be the job of a list class.

**evildotaing** · 11-25-2011

Nice help you had given me, thank you. I thought that only class can create the constructor. Not sure that can use constructor in struct.

Code:

delete current;

After deleting the current from the list, can I use the current for pointer again for transving and to print output using the current to link the info or I need to create a new pointer? And what is the cout << ? ; i had to print to ensure the node had deleted. I try it on my code using current ->info but it crash. What is the output I had to print using cout << and print all of the nodes to ensure the nodes has been deleted. And i only want to delete only the third nodes. I do not want to touch the second nodes.

**iMalc** · 11-25-2011

class members default to private, struct members default to public, that about all the difference there is between them.
Even if you weren't going to use a constructor, you could still write a function to do it and use that

**smokeyangel** · 11-25-2011

Originally Posted by evildotaing

Code:

delete current;

After deleting the current from the list, can I use the current for pointer again for transving and to print output using the current to link the info or I need to create a new pointer? And what is the cout << ? ; i had to print to ensure the node had deleted. I try it on my code using current ->info but it crash. What is the output I had to print using cout << and print all of the nodes to ensure the nodes has been deleted. And i only want to delete only the third nodes. I do not want to touch the second nodes.

"delete current" deletes what current is pointing to. So then "current" points to nothing, as far as you're concerned. If you assign a valid pointer to current, you can carry on using it -- you don't need to actually declare a new pointer.

Code:

    current = first;
    cout << current -> info << endl;
    current = current ->link->link;
    cout << current -> info << endl;
    current = current ->link->link->link;
    cout << current -> info << endl;

So at this point the list is

Code:

5  -->  15  --> 22
^
|
current


    current = current ->link->link;

5  -->  15  --> 22
                ^
                |
            current

(current is meant to point to 22, hopefully it displays ok)

    current = current ->link->link->link;

*bang*! What is current->link? It is NULL. What is NULL->link? A crash!

It does help to draw pictures for this kind of thing. I'd write each number in a box and draw and arrow out of the box to the next number to indicate the link. Then draw arrows to represent "current", "first", "previous" etc. Just do it a step at a time.

To print all the nodes, you could do:

Code:

cout << first->info << endl;
cout << first->link->info  << endl;
cout << first->link->link->info  << endl;

However much better would be to write a function to print all of the nodes, no matter how many there are. You could do this with a loop checking for NULL, or comparing against "last".

**evildotaing** · 11-25-2011

Code:

#include <iostream>

using namespace std;

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

int main()
{
	nodeType * first, * last, *newNode, * current ,*previous;
	first = last = newNode = NULL;

	//int num;

	first = NULL;
	last = NULL;
	cout << "Building a linked list: " << endl;

	newNode = new nodeType;                                  //create a first node
	newNode -> info = 5;
	newNode -> link = NULL;
	cout << "My first node is " <<newNode -> info << endl;   //print the first node = 5

	first = last = newNode;                                  //ensure pointer first and last is in first node
                                        
	newNode = new nodeType;                                  //create a second node                                 
	newNode -> info = 15;
	newNode -> link = NULL;
	cout << "My second node is " <<newNode -> info << endl;  //print the second node = 15
	last->link = newNode;
	last = newNode;

	newNode = new nodeType;                                  //create the third node
	newNode -> info = 10;
	newNode -> link = NULL;
	cout << "My third node is " <<newNode -> info << endl;   //print the third node =10
	last->link = newNode;
	last = newNode;

	newNode = new nodeType;                                 //create a fourth node
	newNode -> info = 22;
	newNode -> link = NULL;
	cout << "My fourth node is " <<newNode -> info << endl; //print the fourth node
	last->link = newNode;
	last = newNode;
	
	cout << "End of building a linked list: " << endl;     //end of building a linked list


	cout << "Transvering " << endl;                         //start to transverse
	current = first;                                        //set current pointer to the first
	
	cout << "Transvering through the first node" << endl;   
	cout << current-> info << endl;                        //5

	cout << "Transvering thorugh the second node" << endl;
	current = first;
	current = current->link ;                              //set current pointer to the second node
	cout << current -> info << endl;                       //15

	cout << "Transvering through the third node" << endl;
	current = first;
	current = current-> link->link;                        //set current pointer to third node
	cout << current -> info << endl;                       //10

	cout << "Transvering through the fourth node" << endl;
	current = first;
	current = current-> link->link->link;                  //set current pointer to fourth node
	cout << current -> info << endl;                       //22
	
	cout << "Transvering through the last node" << endl;   //trying to transverse after the fourth node
	if (current == last)
	{
		cout << "No transvering allowed: " << endl;        //error would be givn
	}
	else
	{
		cout << current -> info << endl;                    //would not print
	}
	cout << endl;
	
	cout << "Transvering back to the first node: " << endl; //back to the first node
	current = first;
	cout << current -> info << endl;


	//Deleting third node
	
	previous = first->link;         // Previous points to 2nd node
	current = previous->link;       // Current points to 3rd node
	previous->link = current->link; // 2nd node's link pointer reset to skip to the 4th node
	delete current;                 // Delete the third node
	current = first;
	cout << current -> info << endl;
	current = current ->link->link;
	cout << current -> info << endl;
	current = current ->link->link->link;
	cout << current -> info << endl;
	system ("pause");
	return 0;
}

This is my latest code. When I try to compile, I received this error "Unhandled exception at 0x00414f0f in assginment 1 das.exe: 0xC0000005: Access violation reading location 0x00000004." causing my program to crash. Did i miss anything in my code and what is exactly wrong. Or is my eletion nodes has some problem or I did not properly create the linked list? And i received this message "error C2018: unknown character '0x60'" if I used the first pointer cout << first->info causing the error.

The problem is now I am using my cout << current->link to set and cout << current->info to print output just like what i had done while I am doing transvering at my code where there are no error yet. But, after deleting the nodes, then the progrm crash while doing the same thing.

**iMalc** · 11-26-2011

That means you dereferenced a NULL pointer. With the debugger attached it will show you exactly which line the problem is on.

**evildotaing** · 11-26-2011

I dun understand what you saying

**evildotaing** · 11-26-2011

Code:

#include <iostream>

using namespace std;

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

int main()
{
	nodeType * first, * last, *newNode, * current ,*previous;
	first = last = newNode = NULL;

	//int num;

	first = NULL;
	last = NULL;
	cout << "Building a linked list: " << endl;

	newNode = new nodeType;                                  //create a first node
	newNode -> info = 5;
	newNode -> link = NULL;
	cout << "My first node is " <<newNode -> info << endl;   //print the first node = 5

	first = last = newNode;                                  //ensure pointer first and last is in first node
                                        
	newNode = new nodeType;                                  //create a second node                                 
	newNode -> info = 15;
	newNode -> link = NULL;
	cout << "My second node is " <<newNode -> info << endl;  //print the second node = 15
	last->link = newNode;
	last = newNode;

	newNode = new nodeType;                                  //create the third node
	newNode -> info = 10;
	newNode -> link = NULL;
	cout << "My third node is " <<newNode -> info << endl;   //print the third node =10
	last->link = newNode;
	last = newNode;

	newNode = new nodeType;                                 //create a fourth node
	newNode -> info = 22;
	newNode -> link = NULL;
	cout << "My fourth node is " <<newNode -> info << endl; //print the fourth node
	last->link = newNode;
	last = newNode;
	
	cout << "End of building a linked list: " << endl;     //end of building a linked list


	cout << "Transvering " << endl;                         //start to transverse
	current = first;                                        //set current pointer to the first
	
	cout << "Transvering through the first node" << endl;   
	cout << current-> info << endl;                        //5

	cout << "Transvering thorugh the second node" << endl;
	current = first;
	current = current->link ;                              //set current pointer to the second node
	cout << current -> info << endl;                       //15

	cout << "Transvering through the third node" << endl;
	current = first;
	current = current-> link->link;                        //set current pointer to third node
	cout << current -> info << endl;                       //10

	cout << "Transvering through the fourth node" << endl;
	current = first;
	current = current-> link->link->link;                  //set current pointer to fourth node
	cout << current -> info << endl;                       //22
	
	cout << "Transvering through the last node" << endl;   //trying to transverse after the fourth node
	if (current == last)
	{
		cout << "No transvering allowed: " << endl;        //error would be givn
	}
	else
	{
		cout << current -> info << endl;                    //would not print
	}
	cout << endl;
	
	cout << "Transvering back to the first node: " << endl; //back to the first node
	current = first;
	cout << current -> info << endl;


	//Deleting third node
	
	previous = first->link;         // Previous points to 2nd node
	current = previous->link;       // Current points to 3rd node
	previous->link = current->link; // 2nd node's link pointer reset to skip to the 4th node
	delete current;                 // Delete the third node
	current = first;
    cout << current -> info << endl;    //print the first numbers
    current = current ->link->link;
    cout << current -> info << endl;     //print second numbers
    current = current ->link->link->link;
    cout << current -> info << endl;     //print fourth nnumbers
	system ("pause");
	return 0;
}

My latest code, still not working. What is wrong with it

**evildotaing** · 11-27-2011

still got problem, anyone help me pls?

**Elysia** · 11-27-2011

Originally Posted by evildotaing

I dun understand what you saying

In the meantime while waiting for an answer, I might suggest you learn about Visual Studio's debugger. Essentially, that is what iMalc is trying to tell you. Use a debugger.

**hk_mp5kpdw** · 11-28-2011

Look at these lines VERY closely and remember that your list only has three numbers in it at this point in your code:

Code:

current = first;
cout << current -> info << endl;    //print the first numbers
current = current ->link->link;
cout << current -> info << endl;     //print second numbers
current = current ->link->link->link;
cout << current -> info << endl;     //print fourth nnumbers

**evildotaing** · 11-28-2011

Code:

#include <iostream>

using namespace std;

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

int main()
{
	nodeType * first, * last, *newNode, * current ,*previous;
	first = last = newNode = NULL;

	

	
	cout << "Building a linked list: " << endl;

	newNode = new nodeType;                                  //create a first node
	newNode -> info = 5;                                     //first node = 5;
	newNode -> link = NULL;                                  //make the first link to NULL first
	cout << "My first node is " <<newNode -> info << endl;   //print the first node = 5
	

	first = last = newNode;                                  //ensure pointer first and last is in first node
                                        
	newNode = new nodeType;                                  //create a second node                                 
	newNode -> info = 15;                                    //second node = 15;
	newNode -> link = NULL;                                  //make the second link to NULL first
	cout << "My second node is " <<newNode -> info << endl;  //print the second node = 15
	last->link = newNode;                                    //link to the second node from the first node
	last = newNode;                                          //set last point to the second node

	newNode = new nodeType;                                  //create the third node
	newNode -> info = 10;                                    //third node = 10;
	newNode -> link = NULL;                                  //make the third link to NULL first
	cout << "My third node is " <<newNode -> info << endl;   //print the third node =1 0
	last->link = newNode;									 //link to the third node from the second node
	last = newNode;

	newNode = new nodeType;                                 //create a fourth node
	newNode -> info = 22;                                   //fourth node = 22;
	newNode -> link = NULL;                                 //make the fourth node link to NULL first
	cout << "My fourth node is " <<newNode -> info << endl; //print the fourth node
	last->link = newNode;
	last = newNode;
	
	cout << "End of building a linked list: " << endl;     //end of building a linked list
	
	//Start of Transvering
	cout << "Transvering " << endl;                         //start to transverse
	current = first;                                        //set current pointer to the first node
	
	cout << "Transvering through the first node" << endl;   
	cout << current-> info << endl;                        //5

	cout << "Transvering thorugh the second node" << endl;
	current = first;                                       //set current back to first node
	current = current->link ;                              //set current pointer to the second node
	cout << current -> info << endl;                       //15

	cout << "Transvering through the third node" << endl;
	current = first;									    //set current back to first node
	current = current-> link->link;                        //set current pointer to third node
	cout << current -> info << endl;                       //10

	cout << "Transvering through the fourth node" << endl;
	current = first;									   //set current back to first node
	current = current-> link->link->link;                  //set current pointer to fourth node
	cout << current -> info << endl;                       //22
	
	cout << "Transvering through the last node" << endl;   //trying to transverse after the fourth node, accessing after from the fourth node
	if (current == last)
	{
		cout << endl;
		cout << "No transvering allowed in fourth node: " << endl;        //error would be given since there are only 4 nodes
		
	}
	else
	{
		cout << current -> info << endl;                    //would not print and go through this else statement since it is not possible
	}
	cout << endl;
	
	cout << "Transvering back to the first node: " << endl; //back to the first node
	cout << endl;
	current = first;                                        //set current back to the first node
	cout << current -> info << endl;                        //print , 5


	//Deleting third node
	
	previous = first->link;         // Previous points to second node
	current = previous->link;       // Current points to third node
	previous->link = current->link; // 2nd node link pointer to link to the 4th node
	delete current;                 // Delete the third node pointing 

	//Print after deleting using transverse
	current = first;                //set the current back to the first node
	cout <<"New first node is " <<  current -> info << endl;    //print the first node, 5
 
	current = first;                                            //set current back to the first node                                  
	current = current ->link;                                   //set current pointing to the second node
	cout << "new Second node is " << current -> info << endl;   //print the second node, , 15

	current = first;                                               //set current pointing back to the first node  
	current = current ->link->link;                                //set current pointing to the fourth node since third node has been deleted
	cout << "New Third node is " << current -> info << endl;       //print 22 instead 0f 10
	cout << "Deletion of the third node is successfully." << endl;

	//Insertion new node between first node and third node
	//newNode = new nodeType;                                  //create a new node
	//newNode -> info = 33;                                     //first node = 33;
	//newNode -> link = NULL;                                  //make the first link to NULL first
	//cout << "My new node is " <<newNode -> info << endl;   //print the first node = 33
	//previous = first;        
	//current = current->link; 
	//previous -> link = newNode;
	//newNode = current;
	//cout << current -> info << endl;
    //cout << current -> info << endl;
	//cout << current -> info << endl;
    
    
	system ("pause");
	return 0;
}

Solve deleting the node. Now I am going to add a node between the first and third node. Do i need to use all of the pointer to do it. I try it on my code but could not work.

**evildotaing** · 11-29-2011

any1 got any idea how to insert it. Do i need to use previous pointer again just like what I had done for deletion.

**evildotaing** · 11-30-2011

Seriously, i dun know what is the problem on my code. I managed to pint 5 , 33 which 33 si the new node number and if I tried to print the next number in linked list, it crash.

Code:

 #include <iostream>

using namespace std;

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

int main()
{
	nodeType * first, * last, *newNode, * current ,*previous;
	first = last = newNode = NULL;

	

	
	cout << "Building a linked list: " << endl;

	newNode = new nodeType;                                  //create a first node
	newNode -> info = 5;                                     //first node = 5;
	newNode -> link = NULL;                                  //make the first link to NULL first
	cout << "My first node is " <<newNode -> info << endl;   //print the first node = 5
	

	first = last = newNode;                                  //ensure pointer first and last is in first node
                                        
	newNode = new nodeType;                                  //create a second node                                 
	newNode -> info = 15;                                    //second node = 15;
	newNode -> link = NULL;                                  //make the second link to NULL first
	cout << "My second node is " <<newNode -> info << endl;  //print the second node = 15
	last->link = newNode;                                    //link to the second node from the first node
	last = newNode;                                          //set last point to the second node

	newNode = new nodeType;                                  //create the third node
	newNode -> info = 10;                                    //third node = 10;
	newNode -> link = NULL;                                  //make the third link to NULL first
	cout << "My third node is " <<newNode -> info << endl;   //print the third node =1 0
	last->link = newNode;									 //link to the third node from the second node
	last = newNode;

	newNode = new nodeType;                                 //create a fourth node
	newNode -> info = 22;                                   //fourth node = 22;
	newNode -> link = NULL;                                 //make the fourth node link to NULL first
	cout << "My fourth node is " <<newNode -> info << endl; //print the fourth node
	last->link = newNode;
	last = newNode;
	
	cout << "End of building a linked list: " << endl;     //end of building a linked list
	
	//Start of Transvering
	
	current = first;                                        //set current pointer to the first node
	
	cout << "Transvering through the first node :" ;   
	cout << current-> info << endl;                        //5

	cout << "Transvering thorugh the second node :" ;
	current = first;                                       //set current back to first node
	current = current->link ;                              //set current pointer to the second node
	cout << current -> info << endl;                       //15

	cout << "Transvering through the third node :" ;
	current = first;									    //set current back to first node
	current = current-> link->link;                        //set current pointer to third node
	cout << current -> info << endl;                       //10

	cout << "Transvering through the fourth node :" ;
	if (current != last)                                        //Prove that the current node is not in last pointer eyt
	{
		current = first;									   //set current back to first node
		current = current-> link->link->link;                  //set current pointer to fourth node
		cout << current -> info << endl;                       //22
	}
	else
	{
		cout << "Should not print this " << endl;           //never print
	}
		
	
	
	cout << "Transvering through the last node" << endl;   //trying to transverse after the fourth node, accessing after from the fourth node
	if (current != last)
	{
		cout << current -> info << endl;                    //would not print and go through this else statement since it is not possible
	}
	else
	{
		cout << endl;
		cout << "No transvering allowed after the fourth node: " << endl;        //error would be given since there are only 4 nodes
	}
	cout << endl;
	
	
	cout << "Transvering back to the first node: "; //back to the first node
	
	current = first;                                        //set current back to the first node
	cout << current -> info << endl;                        //print , 5


	//Deleting third node
	
	previous = first->link;         // Previous points to second node
	current = previous->link;       // Current points to third node
	previous->link = current->link; // 2nd node link pointer to link to the 4th node
	delete current;                 // Delete the third node pointing 

	//Print after deleting using transverse
	current = first;                //set the current back to the first node
	cout <<"New first node is " <<  current -> info << endl;    //print the first node, 5
 
	current = first;                                            //set current back to the first node                                  
	current = current ->link;                                   //set current pointing to the second node
	cout << "New Second node is " << current -> info << endl;   //print the second node, , 15

	current = first;                                               //set current pointing back to the first node  
	current = current ->link->link;                                //set current pointing to the fourth node since third node has been deleted
	cout << "New Third node is " << current -> info << endl;       //print 22 instead 0f 10
	cout << "Deletion of the old third node is successfully." << endl;

	
	
	//Insertion new node between first node and third node
	//newNode = new nodeType;                                  //create a new node
	//newNode -> info = 33;                                     //first node = 33;
	//newNode -> link = NULL;                                  //make the first link to NULL first
	//cout << "My new node is " <<newNode -> info << endl;   //print the first node = 33
	//previous = first;        
	//current = current->link; 
	//previous -> link = newNode;
	//newNode->link = current->link;
	
	//current = first;
	//cout << current -> info << endl;
	
	//current = first;
	//current = current -> link;
   // cout << current -> info << endl;

	//current = first;
	//current = current -> link->link;
    //cout << current -> info << endl;
    
    
	system ("pause");
	return 0;
}

Thread: Help with my linked list

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Help with my linked list

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