foo.cc: In function 'int main()':
foo.cc:30:8: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(a);
        ^
In file included from /usr/include/stdio.h:862:0,
                 from /usr/include/c++/7/cstdio:42,
                 from foo.cc:1:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:232:1: note: declared here
 gets (char *__str)
 ^~~~
foo.cc:28:6: warning: unused variable 'low' [-Wunused-variable]
  int low, high;
      ^~~
foo.cc:28:11: warning: unused variable 'high' [-Wunused-variable]
  int low, high;
           ^~~~
foo.cc:30:6: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result [-Wunused-result]
  gets(a);
  ~~~~^~~
/tmp/cco4GYcb.o: In function `main':
foo.cc:(.text.startup+0x2a): warning: the `gets' function is dangerous and should not be used.

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