foo.cc: In function ‘int main()’:
foo.cc:5:16: error: expected initializer before ‘.’ token
    5 |         int n,a.sum=0;
      |                ^
foo.cc:9:22: error: ‘a’ was not declared in this scope
    9 |                 cin>>a;
      |                      ^
foo.cc:11:17: error: ‘sum’ was not declared in this scope
   11 |                 sum++;
      |                 ^~~
foo.cc:13:15: error: ‘sum’ was not declared in this scope
   13 |         cout<<sum;
      |               ^~~