foo.cc: In function 'void work()':
foo.cc:16:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<ex.size();i++)
              ~^~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:22:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%lld%lld%lld",&n,&m,&q);
  ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
foo.cc:26:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%lld%lld",&x,&y);
   ~~~~~^~~~~~~~~~~~~~~~~~
foo.cc:42:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%lld",&op);
   ~~~~~^~~~~~~~~~~~
foo.cc:46:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    scanf("%lld%lld",&a,&b);
    ~~~~~^~~~~~~~~~~~~~~~~~
foo.cc:53:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    scanf("%lld",&x);
    ~~~~~^~~~~~~~~~~

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