/in/foo.c: In function 'main':
/in/foo.c:16:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
     printf("");
            ^~
/in/foo.c:18:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
     printf("", n);
            ^~
/in/foo.c:23:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
     printf("");
            ^~
/in/foo.c:29:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
     printf("", k);
            ^~