foo.cc: In function 'int main()':
foo.cc:13:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%s %s",s1,s2);
  ~~~~~^~~~~~~~~~~~~~~
foo.cc:14:2: warning: 'i' may be used uninitialized in this function [-Wmaybe-uninitialized]
  for(int i;i<n;i++)
  ^~~

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