/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:28:10: warning: operation on 'rear' may be undefined [-Wsequence-point]
      rear=(++rear)%sz;
      ~~~~^~~~~~~~~~~~
/in/foo.cc:30:13: warning: operation on 'rear' may be undefined [-Wsequence-point]
         rear=(++rear)%sz;
         ~~~~^~~~~~~~~~~~