I am having problems with GUI

I am trying to run the program BasicScreen that I have written and which ran until I tried to embed it in a loop. I have taken it out of the loop and given it the information that it needs. However, running it gives the error message

Error: File: BasicScreen.m Line: 42 Column: 25

Brace indexing into the result of a function call is not supported. Assign the result of

'varargin' to a variable first, then brace index into it.

I MUST ADMIT THAT I HAVE NOT GOT A CLUE WHAT THIS MEANS. HOW DO I GET RID OF THE ERROR? THE CODE IS BELOW, I CAANNOT ATTACH THE GUI. I HAVE PUT IN BOLD THE LINE WITH THE ERROR MESSAGE.

function varargout = BasicScreen
ProbR=0.6;
ProbY=0.4;
ExR=1;
ExY=1;
global x0,y0global ProbR ProbY ExR ExY
global ProbR ProbY ExR ExY
% BASICSCREEN MATLAB code for BasicScreen.fig
%      BASICSCREEN, by itself, creates a new BASICSCREEN or raises the existing
%      singleton*.
%
%      H = BASICSCREEN returns the handle to a new BASICSCREEN or the handle to
%      the existing singleton*.
%
%      BASICSCREEN('CALLBACK',hObject,eventData,handles,...) calls the local
%      function named CALLBACK in BASICSCREEN.M with the given input arguments.
%
%      BASICSCREEN('Property','Value',...) creates a new BASICSCREEN or raises the
%      existing singleton*.  Starting from the left, property value pairs are
%      applied to the GUI before BasicScreen_OpeningFcn gets called.  An
%      unrecognized property name or invalid value makes property application
%      stop.  All inputs are passed to BasicScreen_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
% Edit the above text to modify the response to help BasicScreen
% Last Modified by GUIDE v2.5 23-Apr-2024 11:15:56
% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
    'gui_Singleton',  gui_Singleton, ...
    'gui_OpeningFcn', @BasicScreen_OpeningFcn, ...
    'gui_OutputFcn',  @BasicScreen_OutputFcn, ...
    'gui_LayoutFcn',  [] , ...
    'gui_Callback',   []);
if nargin > 1 && 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 BasicScreen is made visible.
function BasicScreen_OpeningFcn(hObject, eventdata, handles, varargin)
global x0 y0
global ProbR ProbY ExR ExY
disp("in opening")
x0
y0
probR
probY
% Create the RedBox and YellowBox rectangles
% handles.RedBox = rectangle('Position', [x0, y0, probR, 50]);
% handles.YellowBox = rectangle('Position', [x0 + probR, y0, probY, 50]);
% Set the axis limits
% axis([0 100 0 100]);
% Update handles structure
guidata(hObject, handles);
% UIWAIT makes BasicScreen wait for user response (see UIRESUME)
% uiwait(handles.figure1);
% --- Outputs from this function are returned to the command line.
function varargout = BasicScreen_OutputFcn(hObject, eventdata, handles)
global x0 y0
global ProbR ProbY ExR ExY
% 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;
function edit1_Callback(hObject, eventdata, handles)
global x0 y0
global ProbR ProbY ExR ExY
% hObject    handle to edit1 (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 edit1 as text
%        str2double(get(hObject,'String')) returns contents of edit1 as a double
% --- Executes during object creation, after setting all properties.
function edit1_CreateFcn(hObject, eventdata, handles)
global x0 y0
global ProbR ProbY ExR ExY
% hObject    handle to edit1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called
axis([0 100 0 100]);
% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor','white');
end
% --- Executes on slider movement.
function slider1_Callback(hObject, eventdata, handles)
global x0 y0
global ProbR ProbY ExR ExY
% hObject    handle to slider1 (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,'Value') returns position of slider
%        get(hObject,'Min') and get(hObject,'Max') to determine range of slider
disp("in slider")
% probR
% probY
val1=get(handles.slider1,'value');
val=num2str(val1);
set(handles.edit1,'string',val);
x0=90;
y0=24;
disp("clicking on the slider")
% x0
% y0
% probR
% probY
% disp("val then val1")
% val
% val1
axis([0 100 0 100]);
set(handles.RedBox, 'Position', [x0, y0, probR, val1]);
set(handles.YellowBox, 'Position', [x0 + probR, y0, probY, 100 - val1]);
% --- Executes during object creation, after setting all properties.
function slider1_CreateFcn(hObject, eventdata, handles)
% hObject    handle to slider1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called
% Hint: slider controls usually have a light gray background.
if isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor',[.9 .9 .9]);
end

AND HERE IS THE GUI:

Answer 1

[Voss]

Change the main BasicScreen function back to how it was (in particular, it appears you inadvertently removed the text "(varargin)" from the function definition; in general, you should never edit the main function of a GUIDE m-file):

function varargout = BasicScreen(varargin)
% BASICSCREEN MATLAB code for BasicScreen.fig
%      BASICSCREEN, by itself, creates a new BASICSCREEN or raises the existing
%      singleton*.
%
%      H = BASICSCREEN returns the handle to a new BASICSCREEN or the handle to
%      the existing singleton*.
%
%      BASICSCREEN('CALLBACK',hObject,eventData,handles,...) calls the local
%      function named CALLBACK in BASICSCREEN.M with the given input arguments.
%
%      BASICSCREEN('Property','Value',...) creates a new BASICSCREEN or raises the
%      existing singleton*.  Starting from the left, property value pairs are
%      applied to the GUI before BasicScreen_OpeningFcn gets called.  An
%      unrecognized property name or invalid value makes property application
%      stop.  All inputs are passed to BasicScreen_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
% Edit the above text to modify the response to help BasicScreen
% Last Modified by GUIDE v2.5 23-Apr-2024 11:15:56
% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
    'gui_Singleton',  gui_Singleton, ...
    'gui_OpeningFcn', @BasicScreen_OpeningFcn, ...
    'gui_OutputFcn',  @BasicScreen_OutputFcn, ...
    'gui_LayoutFcn',  [] , ...
    'gui_Callback',   []);
if nargin > 1 && 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

And put all your global declarations and other initialization code in BasicScreen_OpeningFcn.

% --- Executes just before BasicScreen is made visible.
function BasicScreen_OpeningFcn(hObject, eventdata, handles, varargin)
global x0 y0
global ProbR ProbY ExR ExY
disp("in opening")

ProbR=0.6;
ProbY=0.4;
ExR=1;
ExY=1;

x0
y0
probR
probY

% Create the RedBox and YellowBox rectangles
% handles.RedBox = rectangle('Position', [x0, y0, probR, 50]);
% handles.YellowBox = rectangle('Position', [x0 + probR, y0, probY, 50]);
% Set the axis limits
% axis([0 100 0 100]);
% Update handles structure
guidata(hObject, handles);
% UIWAIT makes BasicScreen wait for user response (see UIRESUME)
% uiwait(handles.figure1);