/in/foo.c: In function 'main':
/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__;
              ^~~~
/in/foo.c:8:2: warning: implicit declaration of function 'Concat' [-Wimplicit-function-declaration]
  Concat(s1,s2);
  ^~~~~~
/in/foo.c: At top level:
/in/foo.c:12:6: warning: conflicting types for 'Concat'
 void Concat(char a[],char b[])
      ^~~~~~
/in/foo.c:8:2: note: previous implicit declaration of 'Concat' was here
  Concat(s1,s2);
  ^~~~~~
/in/foo.c: In function 'Concat':
/in/foo.c:16:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(a);
  ^~~~
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:17:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(b);
  ^~~~
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__;
              ^~~~
/tmp/cc6yQzjk.o: In function `Concat':
foo.c:(.text+0xd): warning: the `gets' function is dangerous and should not be used.