Segmentation fault in NULL check?

I am getting a segmentation fault while trying to check if some elements are NULL or not. Can anyone help?

    void addEdge(int i, int j) 
{
        if (i >= 0 && j > 0) 
    {
        Node* whereto;
        whereto = linkedAdjacencyList[i];
        if(whereto != NULL)
        {
            while(whereto->adj != NULL)
            {whereto = whereto->adj;}
            whereto->adj = linkedAdjacencyList[j];
        }
        else{linkedAdjacencyList[i]->adj = linkedAdjacencyList[j];}
        whereto = linkedAdjacencyList[j];
        if(whereto != NULL)
        {
            while(whereto->adj != NULL)
            {whe开发者_运维百科reto = whereto->adj;}
            whereto->adj = linkedAdjacencyList[i];
        }
        else{linkedAdjacencyList[j]->adj = linkedAdjacencyList[i];}
            }
    }

help!

EDIT: this is the new code, as per your suggestions, but now there is a segmentation fault immediately when the method is called? i'll post the calling...

int edges;
in >> edges;
g.edges = edges;
for(int i = 0; i < edges; i++)
{
    int first;
    int second;
    in >> first >> second;
    g.addEdge(first, second);
}

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I suggest that linkedAdjacencyList[i] returns NULL, so you are trying to dereference NULL. Just add extra check for NULL :

Node* whereto = NULL;
whereto = linkedAdjacencyList[i];
if (NULL != whereto){
while(whereto->adj != NULL) .....

---

You don't seem to check whether whereto is being initialized properly in whereto = linkedAdjacencyList[i];.

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The expression whereto -> adj != NULL uses whereto as a pointer and dereferences it with adj at its offset from the beginning of the structure or class. If that statement is segfaulting, it means whereto has a bad pointer value. Check what comes out of linkedAdjancencyList[] and don't use it if NULL.

---

Put an if check above the while loop and check whether whereto is NULL.

if(whereto!=NULL){ while(whereto->adj != NULL)......... }