foo.c: In function ‘main’:
foo.c:5:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
    5 |     printf("");
      |            ^~
foo.c:9:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
    9 |     printf("", n);
      |            ^~
foo.c:20:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
   20 |     printf("");
      |            ^~