foo.cc: In function 'int main()':
foo.cc:12:8: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(s);
        ^
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:13:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (i=0; i<=strlen(s); i++){
            ~^~~~~~~~~~~
foo.cc:16:6: warning: suggest explicit braces to avoid ambiguous 'else' [-Wdangling-else]
   if (s[i]==')') 
      ^
foo.cc:19:6: warning: suggest explicit braces to avoid ambiguous 'else' [-Wdangling-else]
   if (s[i]==']') 
      ^
foo.cc:12:6: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result [-Wunused-result]
  gets(s);
  ~~~~^~~
/tmp/ccGSsEen.o: In function `main':
foo.cc:(.text.startup+0x11): 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。