Add 2 numbers in MATLAB, answer to appear in edit text box moment, the numbers are entered in 2 text boxes, without using pushbutton

I am trying to get value in edit3 textbox without using pushbutton

function edit3_Callback(hObject, eventdata, handles)
        % hObject    handle to edit3 (see GCBO)
        % eventdata  reserved - to be defined in a future version of MATLAB
        % handles    structure with handles and user data (see GUIDATA)
        
        % Hints: get(hObject,'String') returns contents of edit3 as text
        %        str2double(get(hObject,'String')) returns contents of edit3 as a double
        a = str2num(get(handles.edit1,'String'));
        b = str2num(get(handles.edit2,'String'));
        c = a + b;
        set(handles.edit3,'String',num2str(c));

Answer 1

[Walter Roberson]

Create the same Callback property for both edit boxes https://www.mathworks.com/help/matlab/ref/matlab.ui.control.uicontrol-properties.html#bt6ck7c-1-Callback

function edit2_Callback(hObject, eventdata, handles)
    a = str2double(get(handles.edit1,'String'));
    b = str2double(get(handles.edit2,'String'));
    if isnan(a) || isnan(b)  %empty or not number
        return;
    end
    c = a + b;
    set(handles.edit3,'String',num2str(c));
end

This callback will be invoked without needing a pushbutton. It does, however, require that the user presses Return in the edit box, or that the user clicks outside the edit box after having entered text in the box.

[Image Analyst]

You could also do it the OOP way:

    a = str2double(handles.edit1.String);
    b = str2double(handles.edit2.String);
    c = a + b;
    handles.edit3.String = num2str(c);

If you want it to compute the moment you type anything in one of the edit fields, I think you might need to set up a timer to periodically get the values every fifth of a second or so, sum them, and send the result to edit3.

[Walter Roberson]

This is "traditional figures". If you fetch the String property of a uicontrol style edit while someone is typing in it, you will not see the updates -- not until they press return or focus on another object. You would have to go in at the Java level in order to get the current String property as someone is typing. Or hook into the KeyPressFcn callback and keep track of everything yourself including correcting for delete keys.

[Avinav Kumar]

Thank you.

 if isnan(a) || isnan(b)  %empty or not number
        return;
    end

If one of the cells is left empty the solution cell still dispalys the same ans (as was in previous step). How to ensure that it updates its value relative to the cell which has number or throws some error message.

[Avinav Kumar]

 a = str2double(handles.edit1.String);
    b = str2double(handles.edit2.String);
    c = a + b;
    handles.edit3.String = num2str(c);

The answer does comes NaN when one cell is empty. If i want to pop out, please enter the value of "something".

[Image Analyst]

if isnan(a)
    warningMessage = sprintf('a is empty.\nPlease put something in the edit field for a.');
    uiwait(errordlg(warningMessage));
    handles.edit3.String = 'Please enter a'
    return;
end

Same for b.

[Avinav Kumar]

Thanks a lot. Its Working.

[Walter Roberson]

 if isnan(a) || isnan(b)  %empty or not number
     handles.edit3.String = 'Inputs are not valid yet';
     return;
 end

[Avinav Kumar]

Thanks a lot. Its Working