/in/foo.c: In function 'main':
/in/foo.c:17:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
     printf("");
            ^~
/in/foo.c:19:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
     printf("", n);
            ^~
/in/foo.c:24:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
     printf("");
            ^~