/in/foo.c: In function 'main':
/in/foo.c:5:15: error: 's2' undeclared (first use in this function)
     char *s1;*s2;
               ^~
/in/foo.c:5:15: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:6:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(s1);
  ^~~~
In file included from /in/foo.c:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.c:7:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(s2);
  ^~~~
In file included from /in/foo.c:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~