• C

# Bubble Sorting a Linked List in C

Hello,

I am having trouble with this function to bubble sort a linked list. I am losing nodes. Could you please help me understand what I am doing wrong and get this right?

Thanks
``````void bubble_sort(item *node)
{
item *first_prev,*first,*second,*temp;
int i, j, n = 1;
bool sorted = false;

//make these 3 pointers point to the head of the list
temp = node;
first = node;
first_prev = node;

//count the number of nodes in the list
while (first->next != NULL)
{
n++;
first= first->next;
}

for (i = 1; i <= n; i++)
{
first = temp;
first_prev = temp;
second = first->next;

for (j=1; j<=(n-i); j++)
{
if (first->val > second->val)
{
if (first == temp)
{
first->next = second->next;
second->next = first;
temp = second;
first = second;
}
else
{
first->next = second->next;
second->next = first;
first_prev->next = second;
first = second;
}
}

first_prev = first;
first = first->next;
second = first->next;
}
}
sorted = true;

PrintList();
}
``````
###### Who is Participating?

Commented:
>> 70                         root = bubble_sort( root );

Make that :

because head is the global pointer that points to the start of the linked list.

>> 304     return first_prev;

Make that :

return temp;

because that's the pointer that points to the beginning of the sorted list.
0

Commented:
What is the type of Linked list you are using?

Linear singly linked list
Circular singly linked list
Two way or doubly linked list
Circular doubly linked list.
0

Commented:
I don't see a problem with your bubble sort algorithm. However, keep in mind that after the sorting, 'temp' points to the first node in the sorted list. 'node' might no longer point to the start of the sorted linked list, but will very likely point to another node in the sorted linked list.

After performing the sort, you need to set temp as the new start node of the linked list.
0

Commented:
How does  PrintList() know where to start?

\
0

Commented:
Infinity08 and ozo are right - the sort-function needs to return the pointer to the first element in the sorted list.

To do so implement the sort function like this:

> item* bubble_sort(item *node)
> {
>  ... // your code
>  return first_prev; // return head item
> }

then call it like this:
> ...
> item* root = new item;
> ...
> root = bubble_sort( root );
> ...

Hope that helps,

ZOPPO
0

Author Commented:
>> 'temp' points to the first node in the sorted list
>> you need to set temp as the new start node of the linked list.

Outside of the loop, after the sorting is over, I set :
node = temp;
first = node;

But still not working. I can't see all nodes sorted.
``````void bubble_sort(item *node)
{
item *first_prev,*first,*second,*temp;
int i, j, n = 1;
bool sorted = false;

//make these 3 pointers point to the head of the list
temp = node;
first = node;
first_prev = node;

//count the number of nodes in the list
while (first->next != NULL)
{
n++;
first= first->next;
}

for (i = 1; i <= n; i++)
{
first = temp;
first_prev = temp;
second = first->next;

for (j=1; j<=(n-i); j++)
{
if (first->val > second->val)
{
if (first == temp)
{
first->next = second->next;
second->next = first;
temp = second;
first = second;
}
else
{
first->next = second->next;
second->next = first;
first_prev->next = second;
first = second;
}
}

first_prev = first;
first = first->next;
second = first->next;

}
}
sorted = true;

node = temp;
first = node;

//PrintList(node);
}
``````
0

Commented:
>> node = temp;

'node' is local to the function. Any change to it will not be visible outside of the function.

You'll need to somehow set the pointer to the first node of the linked list to point to the same node as 'temp'.
0

Commented:
Could you show how you call the bubble_sort function ? (or better yet : could you post the complete code here)
0

Commented:
How do you find the start of the list to see?
0

Author Commented:
>>>>then call it like this:
> ...
> item* root = new item;
> ...
> root = bubble_sort( root );
> ...
0

Author Commented:
>>>then call it like this:
> ...
> item* root = new item;
> ...
> root = bubble_sort( root );
> ...

Isn't this more C++ synthax? With the "new" keyword.
It's not working.
I am getting the following error:
\linkedlistexercice\main.cpp(342) : error C2556: 'item *bubble_sort(item *)' : overloaded function differs only by return type from 'void bubble_sort(item *)'

0

Commented:
Could you post the complete code here ? That'll make things a lot easier ...
0

Commented:
ah, yes, it's C++ - but since you have a 'cpp' file I guess you do C++ and then 'new' is the recommended way to allocate memory.

About the error: I guess you somewhere have a function prototype declaration (maybe in a header or in 'main.cpp') for 'bubble_sort'm somehow like this:

> void bubble_sort( item* );
> // ... any code
> item* bubble_sort( item* node )
> {
>  ...
> }

So the declaration and the implementation use different return types.
0

Author Commented:
>> error C2556: 'item *bubble_sort(item *)' : overloaded function differs only by return type from 'void bubble_sort(item *)'

Sorry, I forgot to change the function prototype on top of the program...
But, still not working.

I am now getting the "Unhandled exception at 0x00411c6e in LinkedListExercice.exe: 0xC0000005: Access violation reading location 0xcdcdcdd1." error...
0

Commented:
We can't guess what your code looks like, so any suggestions we make will likely not work.

As I asked before, could you please post the complete code here. That way, we can make the correct suggestion right away, and immediately solve your problem.
0

Author Commented:
Here is the full code as it stands now...
``````
#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
#include <string.h>

// Structure definition (template)
struct list_el
{
int val;
struct list_el *next;
};
typedef struct list_el item;

item *head = NULL;

void initialize(item*);
void InsertItem();
void DeleteItem();
void FindItem();
//void SortList(item *head, int count);
//void bubble_sort(item *node);
item* bubble_sort(item *node);
//void sort(item *node);
//void swap(item *first, item *first_prev,item *second,item *second_prev);

void main()
{
int choice;
int count = 0;
item* root = new item;

do
{
printf("\n\tWELCOME TO ADVANCED PROGRAMMING\n");
printf("\n\tHere is a taste of working with Linked List in C\n\n");
printf("\n\t1. Insert an item \n");
printf("\n\t2. Delete a particular item\n");
printf("\n\t3. Print all the items\n");
printf("\n\t4. Find an item\n");
printf("\n\t5. Sort List\n");
printf("\n\t6. Quit \n");

scanf("%d",&choice);

switch(choice)
{
case 1:
system("cls");
InsertItem();
break;

case 2:
DeleteItem();
break;

case 3:
break;

case 4:
FindItem();
break;

case 5:
root = bubble_sort( root );

PrintList(root);
break;

case 6:
exit(1);
break;
}
}while(choice != 6);

printf("\n\tThanks for using this program.\n");
getch();
}

void initialize(item *current)
{
printf("\n\tEnter a number: ");
scanf("%d", &current->val);
current->next = NULL;
}

void InsertItem()
{
item *newItem;

newItem =(item*)malloc(sizeof(item));

initialize(newItem);

{
}
else
{
item *current = head;

// Move to the end of the linked list
while(current->next != NULL)
{
current = current->next;
}
if(current->next == NULL)
{
newItem->next = current->next;
current->next = newItem;
}

}
//free(newItem);
}

void DeleteItem()
{
item* current = head;
int nodeNum;
item *newItem,*temp;

printf("\n\tEnter the item whose node you want deleted\n");
scanf("%d",&nodeNum);
newItem = current;

if(current->val == nodeNum)
{
// Deleting the first node
newItem = current;
current = current->next;
free(newItem);
return;
}
else
{
// Deleting an other node
while(newItem->next->next != NULL)
{
if(newItem->next->val == nodeNum)
{
temp = newItem->next;
newItem->next = newItem->next->next;
free(temp);
return;
}
newItem = newItem->next;
}
if(newItem->next->next == NULL && newItem->next->val == nodeNum)
{
// Check condition before deleting the last node
free(newItem->next);
newItem->next = NULL;
return;
}
}
}

{
item* current = head;
printf("\n\t");
while(current!=NULL)
{
printf("%d -->",current->val);
current = current->next;
}
printf("NULL");
}

void FindItem()
{
int NumberToSearch, node = 1;
bool Found = false;
item * current = head;

printf("\n\tEnter the value to search for in the list: ");
scanf("%d", &NumberToSearch);
while(current != NULL)
{

//if value is located in the first node
if (current ->val == NumberToSearch )
{
printf("\n\tValue %d found at node %d", NumberToSearch, node);
Found = true;
break;
}
else
{
current = current->next;
node++;
}
}
if (Found == false)
{
}

}
//void SortList(item *head, int count)
//{
//	//item * head;
//	int i, j/*, count*/;
//	item *p1, *p2, *p3;
//
//
//	for(i = 1; i < count; i++)
//	{
//		p1 = head;
//		p2 = head->next;
//		p3 = p2->next;
//
//		for(j = 1; j <= (count - i); j++)
//		{
//		   if(p2->val < p3->val)
//		   {
//			   p2->next = p3->next;
//			   p3->next = p2;
//			   p1->next = p3;
//			   p1       = p3;
//			   p3       = p2->next;
//		   }
//		   else
//		   {
//			   p1 = p2;
//			   p2 = p3;
//			   p3 = p3->next;
//
//
//		   }
//		}
//	}

//void bubble_sort(item *node)
item* bubble_sort(item *node)
{
item *first_prev,*first,*second,*temp;
int i, j, n = 1;
bool sorted = false;

//make these 3 pointers point to the head of the list
temp = node;
first = node;
first_prev = node;

//count the number of nodes in the list
while (first->next != NULL)
{
n++;
first= first->next;
}

for (i = 1; i <= n; i++)
{
first = temp;
first_prev = temp;
second = first->next;

for (j=1; j<=(n-i); j++)
{
if (first->val > second->val)
{
if (first == temp)
{
first->next = second->next;
second->next = first;
temp = second;
first = second;
}
else
{
first->next = second->next;
second->next = first;
first_prev->next = second;
first = second;
}
}

first_prev = first;
first = first->next;
second = first->next;

}
}
sorted = true;

node = temp;
first = node;

return first_prev;

//PrintList(node);
}
``````
0

Commented:
Oh, and you probably want to remove this line again :

>> 32       item* root = new item;

And :

>> 72                         PrintList(root);

needs to be :

0

Author Commented:
Thank you very much. It's working fine now. That's a relief !!
0

Author Commented:
Just a little worry that I have. I am using malloc() to allocate memory line 96:, I know I should free() the memory to eventually avoid memory leak. But how come I am getting a run-time error if I leave line 120: free(NewItem) in and nothing happens when I comment that out. It just runs ok.
0

Commented:
>> But how come I am getting a run-time error if I leave line 120: free(NewItem) in and nothing happens when I comment that out. It just runs ok.

The memory you allocate is still used after the InsertItem function ends. You've placed the node in the linked list.

The free should be done when you remove the node from the linked list and when you destroy the entire linked list. So, it should be in your DeleteItem function, and at the end of main, you should empty the entire list.
0

Author Commented:
Okay. Thanks heaps.
0
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