foo.cc: In function 'int main()':
foo.cc:12:13: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
     gets(max);
             ^
In file included from /usr/include/stdio.h:862:0,
                 from /usr/include/c++/7/cstdio:42,
                 from /usr/include/c++/7/ext/string_conversions.h:43,
                 from /usr/include/c++/7/bits/basic_string.h:6361,
                 from /usr/include/c++/7/string:52,
                 from /usr/include/c++/7/bits/locale_classes.h:40,
                 from /usr/include/c++/7/bits/ios_base.h:41,
                 from /usr/include/c++/7/ios:42,
                 from /usr/include/c++/7/ostream:38,
                 from /usr/include/c++/7/iostream:39,
                 from foo.cc:1:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:232:1: note: declared here
 gets (char *__str)
 ^~~~
foo.cc: In function 'void zmin(char*)':
foo.cc:36:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<strlen(a);i++)
              ~^~~~~~~~~~
foo.cc:37:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int j=i+1;j<strlen(a);j++)
                 ~^~~~~~~~~~
foo.cc: In function 'void zmax(char*)':
foo.cc:43:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<strlen(a);i++)
              ~^~~~~~~~~~
foo.cc:44:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int j=i+1;j<strlen(a);j++)
                 ~^~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:12:9: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result [-Wunused-result]
     gets(max);
     ~~~~^~~~~
/tmp/ccq8aB9W.o: In function `main':
foo.cc:(.text.startup+0x29): 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。