Radio Button Using Screen Painter

Using screen printer,  how to get the value what i choose from  radio button  . For example, when 'OK_CODE'.
and I want to get the value of radiobutton  and display a message.

if i choose ra radiobutton message s000(38) with 'you choose a' .
esleif rb radiobutton message s000(38) with 'you choose b'.

"Does My code correct or wrong
Please Correct it "
screen

name:   ra and rb
type radiobutton.

Report
data: ra(1) type c, rb(1) type c.

module PAI
when sy-ucomm.

case 'ok_code'
if ra = 'x'.
message s000(38) with 'you choose a'.
  elseif rb= 'x'.
message s000(38) with 'you choose b'.
    endif.
endcase.

Can you give me sample code better than this. thanks