struct queue;

/* return an empty queue */
struct queue *init ( );

/* return true if the queue is empty */
int isEmpty (struct queue *q);

/* add an element to the end of the queue */
struct queue * enqueue (int val, struct queue *q);

/* remove the front of the queue; do nothing if the queue is empty */
struct queue * dequeue (struct queue *q);

/* return the front of the queue; undefined result if the queue is empty */
int front (struct queue *q);

/* print the queue */
void print (struct queue *q);