/in/foo.c: In function 'main':
/in/foo.c:10:2: 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:11:2: 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:29:7: warning: unused variable 's3' [-Wunused-variable]
  char s3[10000];
       ^~
/in/foo.c:28:10: warning: unused variable 'i' [-Wunused-variable]
  int x,y,i,j;
          ^
/tmp/cc4yk2wo.o: In function `main':
foo.c:(.text.startup+0x1c): warning: the `gets' function is dangerous and should not be used.