foo.cc: In function 'int main()':
foo.cc:20:8: warning: ignoring return value of 'int system(const char*)', declared with attribute warn_unused_result [-Wunused-result]
  system("pause");
  ~~~~~~^~~~~~~~~

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