Inherited classes with a deque

[timmy002]

So I'm writing a program for my data structures class. The program description can be found here: http://mathcs.holycross.edu/~csci132/assignments/homework3.html

Everything seems to be working, except when I serve from the front of the queue when the front of the queue at is the maxqueue length.
Here is my code for the serve_front function, disregarding error checking because that is correct

if (front + 1 == maxqueue)
front = 0;
else
front = front + 1;

When I'm calling it in my testing code, here's the call

case 's':
if (test_deque.serve_front() == underflow)
cout << "Deque empty";
else
cout << "Served front of queue";
break;