/in/foo.c: In function 'main':
/in/foo.c:33:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
     printf("");
            ^~
/in/foo.c:35:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
     printf("");
            ^~
/in/foo.c:37:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
     printf("", n1);
            ^~
/in/foo.c:42:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
     printf("", n2);
            ^~