/in/foo.cc: In function 'int main()':
/in/foo.cc:66:6: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
      gets(a[j]);  
      ^~~~
In file included from /usr/include/c++/6/cstdio:42:0,
                 from /usr/include/c++/6/ext/string_conversions.h:43,
                 from /usr/include/c++/6/bits/basic_string.h:5417,
                 from /usr/include/c++/6/string:52,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:66:15: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
      gets(a[j]);  
               ^
In file included from /usr/include/c++/6/cstdio:42:0,
                 from /usr/include/c++/6/ext/string_conversions.h:43,
                 from /usr/include/c++/6/bits/basic_string.h:5417,
                 from /usr/include/c++/6/string:52,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:68:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int m=0;m<strlen(a[j]);m++)//hang
                     ~^~~~~~~~~~~~~
/in/foo.cc:69:20: warning: variable 'a1' set but not used [-Wunused-but-set-variable]
           {   char a1,b='0';
                    ^~
/tmp/ccBfAyMB.o: In function `main':
foo.cc:(.text.startup+0x84): warning: the `gets' function is dangerous and should not be used.