foo.c:4:1: warning: return type defaults to 'int' [-Wimplicit-int]
 xunhuan (int m)
 ^~~~~~~
foo.c: In function 'xunhuan':
foo.c:12:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
foo.c: In function 'main':
foo.c:16:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d",&n);
  ^~~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务