foo.cc: In function 'int main()':
foo.cc:27:23: warning: left operand of comma operator has no effect [-Wunused-value]
         for (len=0;len<=minn(b-a, d-c), str[a+len-1]==str[c+len-1];len++);
                       ^
foo.cc:23:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%s", str);
     ~~~~~^~~~~~~~~~~
foo.cc:30:11: 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 进行评测(github.com/hydro-dev/HydroJudge)

{"receive":"2020-08-06T06:30:21.264Z","handle":"2020-08-06T06:30:21.264Z","cache_start":"2020-08-06T06:30:21.271Z","read_cases":"2020-08-06T06:30:21.379Z","judge":"2020-08-06T06:30:21.381Z","done":"2020-08-06T06:30:27.307Z"}