Queue class check

[nad_scorp]

Here is a queue class that I need someone to check and correct anything wrong since I've got really bored.
I'm using a vacant location to check if queue is empty or full ,but it is not working.


enum Error_code{success,overflow,underflow};
const int maxqueue= 10;
typedef char Queue_entry;

class Queue{
public:
Queue();
bool empty()const;
bool full()const;
Error_code serve();
Error_code append(const Queue_entry &item);
Error_code retrieve(Queue_entry &item)const;
protected:
int front,rear;
Queue_entry entry[maxqueue];
};


Queue::Queue()
{
front=0;
rear=maxqueue -1;
}


Error_code Queue::append (const Queue_entry &item)
{

//if there is space in the queue,item will be added at the end, otherwise an error_code of overflow is returned

if ((rear+1)%max+1==front
return overflow;
else
{rear=((rear+1)==max)?0:rear+1
entry[rear]=item;
return successs;
}


Error_code Queue::serve()
{
//if the queue is not empty, the 1st element is removed,otherwise an error_code of overflow is returned

front=((front+1)==max)?0:front+1
if (rear+1)%max==front
return overflow;
return success;

}


Error_code Queue::retrieve (Queue_entry &item)const
{

if ((rear+1)%max==front)
return underflow;
else
{item=entr[front];
return success;}

}


bool Queue::empty() const
{
if ((rear+1)%maxqueue ==front);
return true ; //empty queue
return false; //not empty
}


bool Queue::full() const
{
((rear+1)%maxqueue +1==front);
return true ; //full queue
return false; //not full
}