Recursion/linked lists

Question

I can't figure out what is wrong with my insert function.

Basically in the main function I ask a user to input an integer, and it should traverse through the list RECURSIVELY and insert the number in order. Please let me know if you need anything else.

When I print out the list it only prints out 0 twice

In the main:
            **This is looped**
    printf("Enter the value you want to insert: ");
    scanf(" %d", &integer);
    current = insert(&head, integer);
    temp = current;

    while(temp)
    {
        printf("%d\n", temp->num);
        temp = temp->next;
    }


node* insert(node** head, int integer)
{
    node* temp = malloc(sizeof(node));
    node* temp1;
    node* new;

    if(*head == NULL)
    {
        temp->num = integer;
        temp->next = *head;
        *head = temp;
    }
    else if((*head)->num > integer)
    {
        temp = *head;
        temp1 = temp->next; //breaks the link
        temp->next = new;   //creates a new node
        new->num = integer;  //adds int
        new->next = temp1;   //links new node to previously broken node
        *head = temp;
    }

    else
        insert(&((*head)->next), integer);

    return(temp);
}

Thanks alot!

Is there any particular reason why you want to do this with recursion? It doesn't seem to make any sense. — Lundin
– Lundin, Commented Mar 18, 2013 at 11:53
@juice look at your if-statement if (*head)->num > integer... see how you use temp->next even though it has not been initialized — AndersK
– AndersK, Commented Mar 18, 2013 at 12:07
Thanks a lot... I caught that in my program awhile ago.. just forgot to update it here. I got it to work for 2 numbers... but then it goes in infinite loop on a 3rd number... still trying to work out why. — ShadyBears
– ShadyBears, Commented Mar 18, 2013 at 12:21

Bojangles · Accepted Answer · 2013-03-18 11:37:46Z

3

if(*head == NULL)
{
    (*head)->next == temp;
    temp->num = integer;
    temp->next = *head;
    *head = temp;
}

this is wrong and will cause an invalid read as *head is NULL and hence (*head)->next is invalid. It'll read from NULL + offset. Where offset depends upon the definition of your node datatype.

edited Mar 18, 2013 at 11:37

Bojangles

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answered Mar 18, 2013 at 11:31

hazzelnuttie

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1 Comment

John3136 Over a year ago

But OP's got an == instead of = (which I think was the intent), so it's an invalid read which is much safer than an invalid write ;-)

eyebrowsoffire · Accepted Answer · 2013-03-18 11:49:05Z

1

while(temp)
{
    printf("%d\n", current->num);
    temp = temp->next;
}

I think you want to be printing out temp->num instead of current->num.

edited Mar 18, 2013 at 11:49

answered Mar 18, 2013 at 11:36

eyebrowsoffire

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1 Comment

ShadyBears Over a year ago

lol that helps... but if i enter 7 and then 3.. it still prints out 0 3

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