How to Hide / Show input fields in selection screen

For that first of all you have to declare 2 parameters and 2 radio button. We assume on click first radio button, first parameter will hide and on select 2nd radio button first parameter will display and 2nd will hide.

First create 2 radio button like below :

parameters: radio_button1 radiobutton group GRP user-command test default 'X',
                          radio_button2 radiobutton group GRP.

You can create 2 different selection screen block also, for each parameter field. Parameter declaration need to be done like below:

selection-screen begin of block b1 with frame title text-001.
         parameters: p_var1 type vbeln modif id GR1.
selection-screen end of block b1.

Here GR1 is the screen group ID. Similarly you can define the 2nd block with screen group ID = GR2. Then write douwn the Hide /Show code in AT SELECTION-SCREEN OUTPUT event.

AT SELECTION-SCREEN OUTPUT.
LOOP AT SCREEN.
  IF SCREEN-GROUP1 = 'GR1' AND radio_button1 EQ 'X'.
    SCREEN-ACTIVE = '0'.
    MODIFY SCREEN.
    CONTINUE.
  ELSEIF SCREEN-GROUP1 = 'GR2' AND radio_button2 EQ 'X'.
    SCREEN-ACTIVE = '0'.
    MODIFY SCREEN.
    CONTINUE.
  ENDIF.
ENDLOOP.

Here, SCREEN-ACTIVE = '0' means screen is not active.
           SCREEN-ACTIVE = '1'. Screen is active