foo.cc: In function 'int main()':
foo.cc:8:20: error: 'o' was not declared in this scope
  double n = 0, m = o, c = o, d = o;
                    ^
foo.cc:11:2: error: 'c' was not declared in this scope
  c = m * 0.8; 
  ^
foo.cc:12:2: error: 'd' was not declared in this scope
  d = n - c;
  ^

[Hydro](https://hydro.ac)提供评测服务