foo.cc: In function ‘int main()’:
foo.cc:17:16: warning: ‘n’ is used uninitialized [-Wuninitialized]
   17 |         int a[n]={ };  //a为空数组， n为数组中n个整数
      |                ^
foo.cc:16:13: note: ‘n’ declared here
   16 |         int n;
      |             ^