foo.cc: In function 'int main()':
foo.cc:7:27: error: 'a' was not declared in this scope
    7 |     for(int i=t;i<=n;i++) a.push_back(i);
      |                           ^
foo.cc:9:19: error: 'a' was not declared in this scope
    9 |     for(int i=0;i<a.size();i++) sum+=a[i];
      |                   ^

[Hydro](https://hydro.ac)提供评测服务