This is a quick test Rcpp module to ensure Rcpp was installed and linked properly to R.  Just run these lines of code in R and the answer should be 9 at the end. 

library(Rcpp)
library(inline)
fx <- cxxfunction(,"",includes=
  ' double add(double c,double d)
   {     double e=0;
         e=c+d;
         return e;
   }
RCPP_MODULE(foo)
   {  function( "add", &add ) ;}
 ', plugin="Rcpp")
foo <- Module("foo",getDynLib(fx))

foo$add(4,5)    #answer is 9