// cqueue.pri

private:
    int  front;          // Subscript of queue front - 1
    int  rear;           // Subscript of queue rear
    char data[QMAX_LENG]; // items in the queue

    // CLASSINV:  At all times, at least one element of "data"
    //            remains unused
    // ABSTRACTION MAP: the front of the queue is data[front+1]
    // and the sequence runs from data[front+1] .. data[rear],
    // wrapping around modulo QMAX_LENG