/in/foo.c: In function 'Concat':
/in/foo.c:7:1: 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:8:1: 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__;
              ^~~~
/in/foo.c: In function 'main':
/in/foo.c:23:1: 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:24:1: 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__;
              ^~~~
/tmp/cccc5qVt.o: In function `Concat':
foo.c:(.text+0xd): warning: the `gets' function is dangerous and should not be used.