foo.cc: In function 'int main()':
foo.cc:9:8: warning: unused variable 'A' [-Wunused-variable]
  char *A;
        ^
foo.cc:10:8: warning: unused variable 'B' [-Wunused-variable]
  char *B;
        ^
foo.cc:11:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%s",s1);
  ~~~~~^~~~~~~~~
foo.cc:12:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%s",s2);
  ~~~~~^~~~~~~~~

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