data.data does not name a type

edit

i create a node in order to publish topic, so i choose std_msgs::Float64 as a type of message sent by my publisher. then i wrote those lines to publish a random message :

std_msgs::Float64 test;
test.data=0.500785;
pub.publish(test);

and that gives me an error : 'test' does not name a type

and : pub.publish(test) does not name a type.

any ideas to solve that? PS: i'm coding in c++ can anyone help me?