/in/foo.cc: In function 'int main()':
/in/foo.cc:11:45: error: no match for 'operator=' (operand types are 'std::basic_ostream<char>::__ostream_type {aka std::basic_ostream<char>}' and 'float')
  cout<<fixed<<setprecision(2)<<x= x * (1 + a);
                                             ^
In file included from /usr/include/c++/6/iostream:39:0,
                 from /in/foo.cc:2:
/usr/include/c++/6/ostream:402:7: note: candidate: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator=(std::basic_ostream<_CharT, _Traits>&&) [with _CharT = char; _Traits = std::char_traits<char>]
       operator=(basic_ostream&& __rhs)
       ^~~~~~~~
/usr/include/c++/6/ostream:402:7: note:   no known conversion for argument 1 from 'float' to 'std::basic_ostream<char>&&'
/in/foo.cc:8:12: warning: unused variable 's' [-Wunused-variable]
  float x,a,s;
            ^