举个简单的例子吧
下面这个用GUIDE生成的m文件里只有一个button，开始时显示start,怎么让它按下后显示stop?
function varargout = biggun(varargin)
% BIGGUN M-file for biggun.fig
% BIGGUN, by itself, creates a new BIGGUN or raises the existing
% singleton*.
%
% H = BIGGUN returns the handle to a new BIGGUN or the handle to
% the existing singleton*.
%
% BIGGUN('CALLBACK',hObject,eventData,handles,...) calls the local
% function named CALLBACK in BIGGUN.M with the given input arguments.
%
% BIGGUN('Property','Value',...) creates a new BIGGUN or raises the
% existing singleton*. Starting from the left, property value pairs are
% applied to the GUI before biggun_OpeningFunction gets called. An
% unrecognized property name or invalid value makes property application
% stop. All inputs are passed to biggun_OpeningFcn via varargin.
%
% *See GUI Options on GUIDE's Tools menu. Choose "GUI allows only one
% instance to run (singleton)".
%
% See also: GUIDE, GUIDATA, GUIHANDLES

% Copyright 2002-2003 The MathWorks, Inc.

% Edit the above text to modify the response to help biggun

% Last Modified by GUIDE v2.5 05-May-2006 21:24:55

% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name', mfilename, ...
'gui_Singleton', gui_Singleton, ...
'gui_OpeningFcn', @biggun_OpeningFcn, ...
'gui_OutputFcn', @biggun_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
% End initialization code - DO NOT EDIT

% --- Executes just before biggun is made visible.
function biggun_OpeningFcn(hObject, eventdata, 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 biggun (see VARARGIN)

% Choose default command line output for biggun
handles.output = hObject;

% Update handles structure
guidata(hObject, handles);

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

% --- Outputs from this function are returned to the command line.
function varargout = biggun_OutputFcn(hObject, eventdata, handles)
% varargout cell array for returning output args (see VARARGOUT);
% hObject handle to figure
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)

% Get default command line output from handles structure
varargout{1} = handles.output;

% --- Executes on button press in pushbutton1.
function pushbutton1_Callback(hObject, eventdata, handles)
% hObject handle to pushbutton1 (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)

% --- Executes on button press in pushbutton1.
function pushbutton1_Callback(hObject, eventdata, handles)
% hObject handle to pushbutton1 (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
set(handes.pushbutton1,'tag','stop');

% --- Executes on button press in pushbutton1.
function pushbutton1_Callback(hObject, eventdata, handles)
% hObject handle to pushbutton1 (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
set(handles.pushbutton1,'string','stop');