How to set noise density

i have edittext box and also checkbox.user can set the value of noise density from 0.1-1.0.what i want to do is, user can key in the value in edittext and after that press the checkbox,so that the noise will add to the image.How to do this?please help me

function chkSaltPepper_Callback(hObject, eventdata, handles)
x = get(handles.TxtNoiseDensity,'String');
d = get(handles.TxtNoiseDensity,'Value');
if isempty(x)
errordlg('Error:Please enter noise density');
else
noiseImage = imnoise(noiseImage,'salt & pepper',d);

function TxtNoiseDensity_Callback(hObject, eventdata, handles)  
input =  str2double(get(hObject,'String'));
if isnan(input)
errordlg('You must enter a numeric value','Invalid Input','modal')
uicontrol(hObject)
return
else
display(input);
end

Answer 1

[Walter Roberson]

function chkSaltPepper_Callback(hObject, eventdata, handles)
x = get(handles.TxtNoiseDensity,'String');
if isempty(x)
  errordlg('Error:Please enter noise density');
else
  d = str2double(x);
  noiseImage = imnoise(noiseImage,'salt & pepper',d);
end