>but don't know how to use cast. can you help me?
That's something that any C++ book or reference will tell you how to use. It would be "cast" or "type cast" in the index.

thank you
:-)

Try reading some of the sticky posts that are labels Read Me: to learn good posting techniques...

class xll
{
public:
int data;
unsigned long link;
};

class xlist
{
xll *head,*tail;
xlist(){head = NULL;tail = NULL}
void insert(int);
};
void xlist :: insert (int ele)
{
xll *node = (xll*) malloc (sizeof(xll));
node->data = ele;
xll *temp = head,*prev = NULL;
while(temp != NULL)
{
next = (xll *) (temp->link ^ (unsigned long) prev);
prev = temp;
temp = next;
}
if(prev == NULL)
head = node;
else
{
node->link ^= (unsigned long) prev ^ (unsigned long) temp;
prev->link ^= (unsigned long) temp ^ (unsigned long) node;
temp->link ^= (unsigned long) prev ^ (unsigned long) node;
}
}