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bananabread76
bananabread76

Reputation: 37

insert node inbetween two others in a linked list

so I want to add inbetween two nodes of a linked list a new node whose data field basically contains the sum of the the previous and the next node. I can't understand why once I enter the while loop I can't get out of it. Any suggestions? Thank you.

Here's my code:

void modify_list (node *head) {
nodo *it = head;
nodo *prev = NULL;
int n_prev = 0;
int n_next = 0;
int sum = 0;
it = it->next;
prev = it;
while (it->next != NULL) {
    it->data = n_next;
    prev->data = n_prev;
    sum = n_next + n_prev;
    node *new;
    new = malloc(sizeof(node));
    if (new == NULL) {
        printf("Error.\n");
        return;
    }
    memset(nuovo, 0, sizeof(node));
    new->data = sum;
    prev->next = new;
    new->next = it;
    sum = 0;
    prev = it;
    it = it->next;
}

}

Upvotes: 0

Views: 87

Answers (2)

sp2danny
sp2danny

Reputation: 7687

May I first suggest breaking your code up in smaller parts
Have a function that inserts a new object
For a singly linked list, this should insert after:

void InsertAfter( Node* n, DATA data )
{
    Node* newnode = malloc(sizeof(Node));
    newnode->data = data;
    newnode->next = n->next;
    n->next = newnode;
}

Then you have a function to find the insert-point
It could be for example

Node* FindLastSmaller( Node* n, DATA data )
{
    while(true)
    {
        if( ! n->next ) return n;
        if( n->next->data > data ) return n;
        n = n->next;
    }
}

Then they become easy to combine:

void InsertSorted( Node* n, DATA data )
{
    Node* inspos = FindLastSmaller(n,data);
    InsertAfter(inspos,data);
}

You can avoid adding special-cases for empty list, if head always
exists, and contains no data. (its a dummy node)

Upvotes: 0

R Sahu
R Sahu

Reputation: 206697

When you start the iteration, you are using:

it = it->next;
prev = it;

it and prev are pointing to the same node. A little while later, you are using:

prev->next = new;

which is the same as:

it->next = new;

That means it->next points to the new node. That means, you never really go past the newly created nodes.

You can fix this by using:

prev = it;
it = it->next;

before the start of the while loop.

I would make that more robust by using:

prev = it;
if ( it != NULL )
{
   it = it->next;
}

At this time, it could be NULL. Change the conditional in the while statement to:

while (it != NULL) {

Upvotes: 1

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