foo.cc: In function 'int main()':
foo.cc:10:10: warning: variable 'c' set but not used [-Wunused-but-set-variable]
     char c;
          ^
foo.cc:20:11: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
      scanf("%s",a[i]+1);
      ~~~~~^~~~~~~~~~~~~

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