/in/foo.c: In function 'main':
/in/foo.c:8:2: 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:9:2: 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__;
              ^~~~
/in/foo.c:10:2: warning: implicit declaration of function 'Concat' [-Wimplicit-function-declaration]
  Concat(s1,s2);
  ^~~~~~
/in/foo.c: At top level:
/in/foo.c:15:6: warning: conflicting types for 'Concat'
 void Concat(char s1[10000],char s2[10000])
      ^~~~~~
/in/foo.c:10:2: note: previous implicit declaration of 'Concat' was here
  Concat(s1,s2);
  ^~~~~~
/tmp/ccX2MPpy.o: In function `main':
foo.c:(.text.startup+0x15): warning: the `gets' function is dangerous and should not be used.