Problems with GUI, unable to use handles to store variables

I am creating a GUI where a user inputs a value and when he presses a pushbutton it runs an external function and displays error messages. I am having trouble with inserting the variable successfully in the GUI coding. I am confused as to where to insert my variable. I have tried handles but unfortunately its not working.

% --- Executes just before Stallfunction is made visible.
function Stallfunction_OpeningFcn(hObject, ~, handles, varargin)
% This function has no output args, see OutputFcn.
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
% varargin   command line arguments to Stallfunction (see VARARGIN)
% Choose default command line output for Stallfunction
handles.user_entry = user_entry;

% Update handles structure
guidata(hObject, handles);

% UIWAIT makes Stallfunction wait for user response (see UIRESUME)
% uiwait(handles.figure1);

I have inserted the variable in the above code, which is 'user_entry' is that correct?

Answer 1

[Achchuthan Ganeshanathan]

This the error I keep receiving

?  ?? Undefined function or variable 'user_entry'.

    Error in ==> Stallfunction>Stallfunction_OpeningFcn at 55
    handles.user_entry = user_entry;

    Error in ==> gui_mainfcn at 221
        feval(gui_State.gui_OpeningFcn, gui_hFigure, [], guidata(gui_hFigure), varargin{:});

    Error in ==> Stallfunction at 42
        gui_mainfcn(gui_State, varargin{:});