foo.cc: In function 'int main()':
foo.cc:8:8: error: 'a' was not declared in this scope
    8 |   cin>>a[i+1];
      |        ^
foo.cc:12:4: error: 'a' was not declared in this scope
   12 |    a[1]=a[k];
      |    ^
foo.cc:15:19: error: array must be initialized with a brace-enclosed initializer
   15 |     int a[i]=a[i-1];
      |              ~~~~~^

[Hydro](https://hydro.ac)提供评测服务