/in/foo.c: In function 'main':
/in/foo.c:18:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
     printf("");  
            ^~
/in/foo.c:22:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
     printf("", n);  
            ^~
/in/foo.c:27:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
     printf("");  
            ^~
/in/foo.c:30:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
     printf("");  
            ^~