/in/foo.cc: In function 'int main()':
/in/foo.cc:7:17: warning: format '%lf' expects argument of type 'double', but argument 2 has type 'double*' [-Wformat=]
  printf("%lf",&r)
                 ^
/in/foo.cc:8:2: error: expected ';' before 'a'
  a=r*2;
  ^