Matlab - sentencia if en edit text guide matlab

function varargout = leer_un_dato_acotado(varargin)

gui_Singleton = 1;

gui_State = struct('gui_Name',       mfilename, ...

                   'gui_Singleton',  gui_Singleton, ...

                   'gui_OpeningFcn', @leer_un_dato_acotado_OpeningFcn, ...

                   'gui_OutputFcn',  @leer_un_dato_acotado_OutputFcn, ...

                   'gui_LayoutFcn',  [] , ...

                   'gui_Callback',   []);

if nargin && ischar(varargin{1})

    gui_State.gui_Callback = str2func(varargin{1});

end

if nargout

    [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});

else

    gui_mainfcn(gui_State, varargin{:});

end

function leer_un_dato_acotado_OpeningFcn(hObject, eventdata, handles, varargin)

handles.output = hObject;

guidata(hObject, handles);

function varargout = leer_un_dato_acotado_OutputFcn(hObject, eventdata, handles)

varargout{1} = handles.output;

function edit1_Callback(hObject, eventdata, handles)

while 1

    a=str2double(get(hObject,'String'));

    if a<3 || a>100

        set(hObject,'string','');

    else

        break;

    end

end