/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: In function 'Concat':
/in/foo.c:12:16: warning: unused variable 'b' [-Wunused-variable]
  int i,k=0,a=0,b;
                ^
/in/foo.c:12:12: warning: unused variable 'a' [-Wunused-variable]
  int i,k=0,a=0,b;
            ^
/tmp/ccLj0Ld8.o: In function `main':
foo.c:(.text.startup+0x15): warning: the `gets' function is dangerous and should not be used.