foo.cc: In function 'int main()':
foo.cc:22:7: warning: unused variable 'str' [-Wunused-variable]
  char str[20000];
       ^~~
foo.cc:23:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
  freopen("data.txt", "r", stdin);
  ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
foo.cc: In function 'int Count()':
foo.cc:17:16: warning: 'cntd' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return cntd - cntx; 
                ^~~~

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