foo.cc: In function 'void shangqian(int, int)':
foo.cc:29:12: warning: operation on 'i' may be undefined [-Wsequence-point]
    b[i]=b[i++];
           ~^~
foo.cc:32:11: warning: 'x' may be used uninitialized in this function [-Wmaybe-uninitialized]
  cout<<x<<" ";
           ^~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。