foo.cc: In function 'int main()':
foo.cc:29:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%lf%lf%lf%lf",&a,&b,&c,&d);
     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~

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

{"receive":"2020-08-09T19:34:34.731Z","handle":"2020-08-09T19:34:34.731Z","cache_start":"2020-08-09T19:34:34.739Z","read_cases":"2020-08-09T19:34:34.871Z","judge":"2020-08-09T19:34:34.874Z","done":"2020-08-09T19:34:35.041Z"}