Well, I figured it out myself the best way I knew how: I just stuck a vertical quit button in to main() function:
entry = gtk_entry_new_with_max_length (50);
gtk_signal_connect (GTK_OBJECT (entry), "activate",
GTK_SIGNAL_FUNC (enter_callback), entry);
hbox = gtk_hbox_new (FALSE, 0);
gtk_container_add (GTK_CONTAINER (vbox), hbox);
button = gtk_button_new_with_label ("Quit");
gtk_signal_connect_object (GTK_OBJECT (button), "clicked",
gtk_box_pack_start (GTK_BOX (vbox), button, TRUE, TRUE, 0);
GTK_WIDGET_SET_FLAGS (button, GTK_CAN_DEFAULT);
The "enter_callback()" fn seems to have some surplus code ... gotta check that.
This works for now, but I would very much appreciate it if anybody could clean up any unnecessary code. I'm learning by actually writing .... even if it means stumbling.