Not getting Error message

I am trying to get an error message if my a value is left empty by user. But i am not getting the same. If someone can help.My code is as follows.

function Run_Callback(hObject, eventdata, handles)
% hObject    handle to Run (see GCBO)
% eventdata  reserved - to be defined in edit1 future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
a=str2double(get(handles.edit1,'string'));
b=str2double(get(handles.edit2,'string'));
c=str2double(get(handles.edit3,'string'));
d=str2double(get(handles.edit4,'string'));
e=str2double(get(handles.edit5,'string'));
f=str2double(get(handles.edit6,'string'));
g=str2double(get(handles.edit7,'string'));
h = a *((b/c)*(d/e)^2*(f/g))^(1/5);
if isempty(a)
errordlg('Please enter value ofDreference','Error Code I');
else
set(handles.edit8,'string',num2str(h));
end

Answer 1

[Walter Roberson]

AnEmptyString = '';
str2double(AnEmptyString)

ans = NaN

When you str2double() something empty, you get NaN, not empty. You need to check the result of the get() if you want to distinguish between the user entering nothing, or the user entering 'NaN', or the user entering something that is not number-like.