/in/foo.cc: In function 'int main()':
/in/foo.cc:19:3: error: 'total' was not declared in this scope
   total+ = fenshu(i);
   ^~~~~
/in/foo.cc:19:10: error: expected primary-expression before '=' token
   total+ = fenshu(i);
          ^
/in/foo.cc:21:10: error: 'total' was not declared in this scope
  cout << total;
          ^~~~~