How to change a cell table from numeric to string?

Hi, i'm creating a GUI on Matlab and I would like to add a table and be able with pushbuttons to add/delete rows and columns (working with callback functions). This part of my GUI works fine. But my cells are all numeric cells only, and when I write letters, it gives me "NaN". Can someone help? Here is the code:

% --- Executes on button press in pushbutton7.
*% ADD ROW %*
function pushbutton7_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton7 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
data = get(handles.uitable, 'data');
data(end+1,:) = 0;
set(handles.uitable, 'data', data);

% --- Executes on button press in pushbutton8.

*% ADD COLUMN %*
function pushbutton8_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton8 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
data = get(handles.uitable, 'data');
data(:,end+1) = 0;
set(handles.uitable, 'data', data);

% --- Executes when entered data in editable cell(s) in uitable.
*% ADD TABLE %*
function uitable_CellEditCallback(hObject, eventdata, handles)
%hObject    handle to uitable (see GCBO)
%eventdata  structure with the following fields (see MATLAB.UI.CONTROL.TABLE)
%Indices: row and column indices of the cell(s) edited
%PreviousData: previous data for the cell(s) edited
%EditData: string(s) entered by the user
%NewData: EditData or its converted form set on the Data property. Empty if Data was not changed
%Error: error string when failed to convert EditData to appropriate value for Data
% handles    structure with handles and user data (see GUIDATA)
data = get(hObject,'data');
display(data);

Answer 1

[Walter Roberson]

Use the property inspector on the uitable to set the ColumnFormat property to 'string'.

[MM BS]

I have the same problem but I dont use Guide : I do it manully (directly) :

a={};
for i=1:10
  a{i,5}=true;
end
h = uitable('data',a, ...
     'columnformat', {'numeric','char','logical',{'str1','str2'},'logical'}, ...
     'columneditable',true);

What I can do to impose to matlab to recongnize the string when it's a string format on the culmn?