Sorting a string linked list

This is a discussion on Sorting a string linked list within the C Programming forums, part of the General Programming Boards category; I want to print out a sorted string linked list but my codes sort in the order of entry. such ...

  1. #1
    Brak BoneXXX's Avatar
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    Sorting a string linked list

    I want to print out a sorted string linked list but my codes sort in the order of entry.
    such as :
    Code:
    Input : e a g c
    Outout : e a g c
    How can I convert my codes to insert the inputs in actual alphabetic sorted order. Could you help me please?

    Code:
    void insert_in_order(char *n, node_ptr list)
    {
    	node_ptr before = list;
    	node_ptr new_node = (node_ptr)malloc(sizeof(struct node));
    	new_node->name = n;
    
    	while(before->next && (before->next->name < n))
    	{
    		before = before->next;
    	}
    	new_node->next = before->next;
    	before->next = new_node;
    }
    “Example isn't another way to teach, it is the only way to teach” Albert Einstein

  2. #2
    Lean Mean Coding Machine KONI's Avatar
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    1. Shouldn't you be comparing n with before->name instead of before->next->name ?
    2. Use strcmp()

  3. #3
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    In order to sort the list, you need to do comparisons, yeah? Unless your names are going to have just one letter, you'll want to use a library function like strcmp(), to take care of the letter by letter comparisons involved.

    Why don't you start with a simple Bubble sort (you can get the algo from Wiki or zillions of web sites), and study it, see what it's all about.

    Then make the adjustments in that code that need to be made so it will work with a linked list, instead of the usual, array.

    Sorting is one of the most common activities for all kinds of programs to do. Learn all you can about it, including why Bubble sort is not a good sorter if you have a good deal of data that needs to be sorted.

    Adak
    Last edited by Adak; 04-28-2007 at 01:44 AM.

  4. #4
    Brak BoneXXX's Avatar
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    Thanks for the replies.At this point I need bit more effective. Am I on the right right track, if I am not can you put me on the right track?

    I am getting
    Code:
    list.c:59: warning: passing arg 2 of `__builtin_strcmp' from incompatible pointer type
    list.c:59
    Code:
    while(strcmp(previous, new_node ) > 0 && strcmp(current, new_node) < 0)
    Rest of the codes:
    Code:
    void insert_in_order(char *n, node_ptr list)
    {
    	node_ptr previous = list;
    	node_ptr current = list->next;
    	node_ptr new_node = (node_ptr)malloc(sizeof(struct node));
    	new_node->name = n;
    	
    	if(current == NULL)
    	{
    		new_node->next = list->next;
    		list->next = new_node;
    		
    	}
    	while (current != NULL)
    	{
    		while(strcmp(previous, new_node ) > 0 && strcmp(current, new_node) < 0)
    		{
    			previous->next = new_node;
    			new_node->next = current;
    			break;	
    		}
    		previous = current;
    		current = current->next;
    	}
    }
    Last edited by BoneXXX; 04-29-2007 at 01:11 AM.
    “Example isn't another way to teach, it is the only way to teach” Albert Einstein

  5. #5
    Lean Mean Coding Machine KONI's Avatar
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    strcmp() compares strings, its two parameters need to be of type char* and not of type node_ptr

  6. #6
    Brak BoneXXX's Avatar
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    Thanks for the reply. The compiling problem is fixed.

    Unfortunately it didn't sorted in the way that I wanted which is in an alphabetic way.

    My input was : a b z c
    the output : c z b a
    “Example isn't another way to teach, it is the only way to teach” Albert Einstein

  7. #7
    CSharpener vart's Avatar
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    your internal while is executes 0 or 1 time - use if instead

    What if the new_node should be insearted after the last one? Where do you do it?
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  8. #8
    Brak BoneXXX's Avatar
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    but whit the while loop I wanted to compare the previous and the current nodes find the right place. Such as 1 2 4 5 - 3 is going to be inserted between 2 and 4. I was trying to do this.
    “Example isn't another way to teach, it is the only way to teach” Albert Einstein

  9. #9
    Brak BoneXXX's Avatar
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    I sorted out now, it compiles in the right alphabetic order but it can take the same input more than once. Is there any idea?

    Code:
    void insert_in_order(char *n, node_ptr list)
    {
        node_ptr before = list;
        node_ptr new_node = (node_ptr) malloc(sizeof(struct node));
        new_node->name = n;
    
        /* Move along list until right place is found, looking for node after
           which new node should go */
        while(before->next && (strcmp(before->next->name, new_node->name) < 0))
        {
            before = before->next;
        }
    
        new_node->next = before->next;
        before->next = new_node;
    }
    “Example isn't another way to teach, it is the only way to teach” Albert Einstein

  10. #10
    ATH0 quzah's Avatar
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    Change it to <= instead of just < and it will then match identical strings also.


    Quzah.
    Hope is the first step on the road to disappointment.

  11. #11
    Brak BoneXXX's Avatar
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    I tried it with && (strcmp(before->next->name, new_node->name) == 0) but I will try your suggestion and let you know. Thanks.
    “Example isn't another way to teach, it is the only way to teach” Albert Einstein

  12. #12
    Brak BoneXXX's Avatar
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    Quote Originally Posted by quzah View Post
    Change it to <= instead of just < and it will then match identical strings also.


    Quzah.
    it didn't work Can it be related to my main program.
    Code:
    			printf("Enter a name:\n");
    			scanf("&#37;s",buffer);
    			n=(char*)malloc(strlen(buffer));
    			strcpy(n,buffer);
    			delete_it(n,the_list);
    Last edited by BoneXXX; 04-30-2007 at 05:12 AM.
    “Example isn't another way to teach, it is the only way to teach” Albert Einstein

  13. #13
    Brak BoneXXX's Avatar
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    It is fixed. I have another question now. When I want to delete a name from the list I get a segmentation fault. At least could you help me on this?

    calling the function:
    Code:
    	printf("Enter an unit name but not more than 100 characters:\n");
    	scanf("&#37;s",buffer);
    	n=(char*)malloc(strlen(buffer)+1);
    	strcpy(n,buffer);
    	delete_it(n,the_list);
    The Function:
    Code:
    /*Function to delete  unit from the list*/
    void delete_it(char *n, node_ptr list)
    {
    	node_ptr before = list;
    	node_ptr current = list->next;
    	node_ptr new_node = (node_ptr) malloc(sizeof(struct node));
    	
    	while(current != NULL)
    	{
    		if(strcmp(before->next->name, new_node->name) == 0)
    		{
    			before->next = current->next;
    			free(current);
    		}
    		else
    		{
    			before = current;
    			current = current->next;
    		}
    	}
    	return;
    }
    “Example isn't another way to teach, it is the only way to teach” Albert Einstein

  14. #14
    Woof, woof! zacs7's Avatar
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    No need to cast malloc,

    Me thinks first bit of code should be:

    Code:
    char buffer[128];
    /*
    ...
    */
    
    printf("Enter an unit name but not more than 100 characters:\n");
    puts("Enter an unit name");
    fgets(buffer, sizeof(buffer), stdin);
    delete_it(buffer, the_list);
    /* um, why were you moving buffer from the stack to the heap ? */

  15. #15
    Brak BoneXXX's Avatar
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    Thanks for the reply but in your codes nothing goes into the function. In my codes everything is fine until "delete_it(n,the_list);", when it comes to this point I get a segmentation fault.
    “Example isn't another way to teach, it is the only way to teach” Albert Einstein

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