foo.c: In function 'xf':
foo.c:11:1: warning: control reaches end of non-void function [-Wreturn-type]
   11 | }
      | ^
foo.c: In function 'main':
foo.c:15:8: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   15 |  int x;scanf("%d",&x);
      |        ^~~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务