foo.c: In function 'main':
foo.c:15:16: error: 'k' undeclared (first use in this function)
   15 |  if(n%2==1)  a[k][k]=v;
      |                ^
foo.c:15:16: note: each undeclared identifier is reported only once for each function it appears in
foo.c:6:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
    6 |  scanf("%d",&n);
      |  ^~~~~~~~~~~~~~

正在同步测试数据，请稍后
[Hydro](https://hydro.ac)提供评测服务