SQL & PL/SQL

Hi

I'm using Oracle SQL Developer . I want to take input from the user and display it .

The user should be asked "Please enter your User ID"
I read about Prompt and accept from the blogs in the forum but still not being able to produce the prompt with the correct message .
The user id is a charater and I need to print it .But I'm getting some error . Please correct me .
I'm pasting the code which I had written

declare
ACCEPT USERID CHAR PROMPT 'PLEASE ENTER YOUR USER ID: '
Begin
USERID := '&USERID';
DBMS_OUTPUT.PUT_LINE(USERID);
END;

It is giving a prompt as USERID and when I put value into it there is an error .

Warm Regards
Rahul