foo.c: In function 'main':
foo.c:9:15: error: 'x' undeclared (first use in this function)
    9 |   printf("%d",x);
      |               ^
foo.c:9:15: note: each undeclared identifier is reported only once for each function it appears in
foo.c:4:6: warning: variable 'a' set but not used [-Wunused-but-set-variable]
    4 |  int a,n;
      |      ^
foo.c:5:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
    5 |  scanf("%d",&n);
      |  ^~~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务