foo.cc: In function ‘int main()’:
foo.cc:6:16: error: conflicting declaration ‘double n’
    6 |         double n,s;
      |                ^
foo.cc:5:13: note: previous declaration as ‘int n’
    5 |         int n,i;
      |             ^
foo.cc:10:22: error: ‘a’ was not declared in this scope
   10 |                 cin>>a;
      |                      ^