var txtIn,txtOut,butExec:int

procedure setIn(x:string)
   ...code...
end setIn

procedure setOut (x:string)
    ...code...
end setOut

procedure execute
    var x:string := GUI.GetText(txtIn)
    ...code...
end execute

txtIn:= GUI.CreateTextField(x,y,width,"text",setIn())
txtOut := GUI.CreateTextField(x,y,width,"text",setOut)
GUI.Disable(txtOut) %you can remove this it just makes them unable to change the output u can use a textbox instead also.

butExec := GUI.CreateButton (x,y,width,"text",execute)

loop
    GUI.ProcessEvent
end loop