C++ list is working but giving error Thread 1: EXC_BAD_ACCESS (code=1, address=0x8)

Hi Guys i am facing this list problem where i want to clone a list with random pointers. But my code is giving me this error while cloning pointers. here i am adding only the function code but i am also attaching the link for full code. the error is

Thread 1: EXC_BAD_ACCESS (code=1, address=0x8)

Node *createAnotherList(Node *head){
Node *temp = head, *start = head;
Node *firstPointer;
int count = 0;

while(temp != NULL){
    Node *newNode = new Node;
    newNode->data = temp->data;
    newNode->random = NULL;
    newNode->next = temp->next;
    temp->next = newNode;
    if(count == 0){
        firstPointer = newNode;
        count++;
    }
    temp = newNode->next;
}

//    printList(list1);

while(start != NULL){
    cout << start->data << " ";
    if(start->next)
        start->next->random = start->random->next;
    start = start->next ? start->next->next : start->next;

}

    return head;
}

i am getting error in 2nd while loop

start->next->random = start->random->next;

if someone knows what is the error please help me. and for more info please check the code from the link and error line is LINE 74

enter link description here