linked list access violation writing location - c++

Question

I'm writing a program doing LSD radix sort with SSN. The program will parse the number into 3 digits and do 3 passes. Each pass I store the number into corresponding array element bucket[]; if there's a duplicate, I create a linked list in that location and store the duplicated one behind the one that's already there. The code breaks when I try to insert in the end of the linked list.
EDIT new error message
class node
{
public:
node(int n, node *p){data=n;next=p;}
int data;
node *next;
};
void genData(int *dta, int n)
{
for(int i=0; i < n; i++)// generate the social security numbers at random
dta[i] = rand()%889 + 111 + 1000*(rand()%889 + 111) + 1000000* (rand()%889 + 111);
}
int radixSort(int *dta, int n, int *out)
{
// the dta array contains the data to be sorted.
// n is the number of data items in the array
// out is the array to put the sorted data
node *bucket[1000]; // declare an array of 1000 linked lists (head pointers)
int count = 0; // use this to count the instructions to graph the big-o
for(int i = 0; i < n; i++)out[i] = dta[i];
for (int pass = 0; pass < 3; pass++)
{
for (int j = 0; j < 1000; j++){
bucket[j] = NULL;
}
delete bucket;
delete[]bucket;
for (int i = 0; i < n; i++){
int index=0;
switch (pass)
{
case 0:
index = out[i] % 1000;
case 1:
index = (out[i]/1000) % 1000;
case 2:
index = out[i] / 1000000;
};
if (bucket[index] = NULL){
bucket[index] = new node(out[i], NULL);
}
else{
node *cur=bucket[index];
while (cur->next!= nullptr){ //****access violation reading location
cur = cur->next;
}
node *ptr = new node(out[i], NULL);
cur->next = ptr;
}
}
int idx = 0;
for (int i = 0; i < 1000; i++){
if (bucket[i] == NULL) continue;
else{
out[idx] = bucket[i]->data;
idx++;
count++;
}
}
}

Answer 1

Theres a number of problems in your code:
In your switch-statement you have lines like index == out[i] % 1000;Those do a comparison and i doubt this is what you want. Assignments use single =
Your initialization for (int j = 0; j < 1000; j++){bucket[j] = NULL;} does not check if theres already a pointer in it - this will cause memory leaks after the first pass. Remember: Every new needs a delete.
And thats what is probably breaking your code: while (cur!= NULL){cur = cur->next;} exits the while-loop once cur is the nullptr - which means trying to dereference it 2 lines later is trying to dereference the nullptr and a bad idea. What you probably want to check in order to get your last element is `while(cur->next != nullptr)
And just as a note: if your compiler supports nullptr its a good idea to use it, even if you might need to enable C++11 via appropriate flags.