/in/foo.cc: In function 'int main()':
/in/foo.cc:23:8: warning: operation on 'front' may be undefined [-Wsequence-point]
   front=(++front)%sz;
   ~~~~~^~~~~~~~~~~~~
/in/foo.cc:28:14: warning: operation on 'rear' may be undefined [-Wsequence-point]
          rear=(++rear)%sz;
          ~~~~^~~~~~~~~~~~
/in/foo.cc:30:21: warning: operation on 'rear' may be undefined [-Wsequence-point]
                 rear=(++rear)%sz;
                 ~~~~^~~~~~~~~~~~