/in/foo.c: In function 'main':
/in/foo.c:27:2: 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:27:7: warning: passing argument 1 of 'gets' from incompatible pointer type [-Wincompatible-pointer-types]
  gets(s1);
       ^~
In file included from /in/foo.c:1:0:
/usr/include/stdio.h:640:14: note: expected 'char *' but argument is of type 'int *'
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.c:28:2: 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:28:7: warning: passing argument 1 of 'gets' from incompatible pointer type [-Wincompatible-pointer-types]
  gets(s2);
       ^~
In file included from /in/foo.c:1:0:
/usr/include/stdio.h:640:14: note: expected 'char *' but argument is of type 'int *'
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.c:29:9: warning: passing argument 1 of 'concat' from incompatible pointer type [-Wincompatible-pointer-types]
  concat(s1,s2);
         ^~
/in/foo.c:3:6: note: expected 'char *' but argument is of type 'int *'
 void concat(char b[],char c[])
      ^~~~~~
/in/foo.c:29:12: warning: passing argument 2 of 'concat' from incompatible pointer type [-Wincompatible-pointer-types]
  concat(s1,s2);
            ^~
/in/foo.c:3:6: note: expected 'char *' but argument is of type 'int *'
 void concat(char b[],char c[])
      ^~~~~~
/tmp/cc2nVnlE.o: In function `main':
foo.c:(.text.startup+0x15): warning: the `gets' function is dangerous and should not be used.