Keep track of variable value in gui

I am designing a program with GUIDE that simulates a coin toss game. It has 3 components:

+ A static text box, called text1 to keep track of your current balance.

+ An editable text box, called text2 so that you can type in the amount you want to bet.

+ A push button, called button1 to simulate a coin toss.

This is what I have tried:

 %first, I used the Property Inspector on text1 to change its string from "Static text" to "1000"
 %This way, the player starts the game with $1000
Current_Balance=str2double(get(handles.text1,'string'));
%Then, I acquire the bet amount from text2:
Bet=str2double(get(handles.text2,'string'));
%Next, to simulate a coin toss:
result=binornd(1,0.5);
if result==0;
Current_Balance=Current_Balance - Bet;
else Current_Balance=Current_Balance + Bet;
end
%I tried to update the value of Current_Balance with the next code.
%This is where the error message pops up;
set(handles.text1,'string',Current_Balance);

What I am trying to do is to calculate and show the new result Current_Balance each time a button is pressed. Any ideas?

[Jan]

You mention an error message, but keep the message as your secret. Please reveal it, such that we do not have to guess it. :-)

Answer 1

[Jan]

Current_Balance = str2double(get(handles.text1, 'string'));

Now Current_Balance is a double array, most likely a scalar. You perform some arithmetic operations with it, and then:

set(handles.text1, 'string', Current_Balance);

tries to set the 'string' value with a double scalar. I guess you want:

set(handles.text1, 'string', num2str(Current_Balance));

or

set(handles.text1, 'string', sprintf('%.2f', Current_Balance));

to provide a string.

[Nguyen Quang]

Thank you very much for your help. I am sorry that I only posted part of the program, because I thought it was the one part that caused the problem. I ended up getting a wrong answer for that. I apologize for wasting your time.

Anyway, this is the full game:

+ A static text box, called text1 to keep track of your current balance (just like the previous one). The string value is changed from "Static text" to "1000"(so that players start with $1000);

+ An editable text box, called text2 so that you can type in the amount you want to bet ((just like the previous one);).

+ A push button, called buttonA, lets you join a coin toss game.

+ Another push button, called buttonB, lets you join a game of dice.

+ A third button, buttonC, simulates the result and updates your Current Balance

The game goes as follow:

 %Press buttonA to play coin game  
  function buttonA_Callback(hObject, eventdata, handles)  
  Current_Balance=str2double(get(handles.text1,'string'));  
  Bet=str2double(get(handles.text2,'string'));  
  result=binornd(1,0.5);  
  if result==0;  
  Current_Balance=Current_Balance - Bet;  
  else Current_Balance=Current_Balance + Bet;  
  end

%Press buttonB to play dice game  
function buttonB_Callback(hObject, eventdata, handles)  
Current_Balance=str2double(get(handles.text1,'string'));  
Bet=str2double(get(handles.text2,'string'));  
result=binornd(1,0.1666);   
if result==0  
Current_Balance=Current_Balance - 3*Bet;  
else Current_Balance=Current_Balance + 3*Bet;  
end

%Press button C to show the result  
function buttonC_Callback(hObject, eventdata, handles)
set (handles.text1,'string',Current_Balance);

Whenever I press buttonC, Matlab shows the error message as follow:

??? Undefined function or variable 'Current_Balance'.
Error in ==> untitled>buttonC_Callback at 127
set(handles.text1, 'string', Current_Balance);
Error in ==> gui_mainfcn at 96
      feval(varargin{:});
Error in ==> untitled at 42
  gui_mainfcn(gui_State, varargin{:});
Error in ==>
@(hObject,eventdata)untitled('buttonC_Callback',hObject,eventdata,guidata(hObject))
??? Error while evaluating uicontrol Callback

I don't know what the problem is. I guess it has to do with making sure that either buttonA or buttonB is pushed before button C is pushed. Can you guys please help me, please?

[Jan]

The error message is clear: In this piece of code:

function buttonC_Callback(hObject, eventdata, handles)
set(handles.text1,'string',Current_Balance);

The variable "Current_Balance" is not defined. It was created in another callback, but the variables are not shared between functions.

The topic of sharing variables between callback is discussed frequently in this forum, therefore searching in the forum is a good idea. See e.g.:

• https://www.mathworks.com/matlabcentral/answers/102591-what-is-the-difference-between-application-data-guidata-and-userdata-in-matlab
• https://www.mathworks.com/matlabcentral/answers/330303-why-is-not-the-handles-variable-updated
• https://www.mathworks.com/matlabcentral/answers/38419-get-value-from-popup-menu-and-use-it-in-different-function
• ...

Answer 2

[Nguyen Quang]

Thanks for the article you recommended.I managed solved the problem myself. The solution is to declare Current_Balance a global variable at the beginning of each button callback, like this:

%Press buttonA to play coin game
function buttonA_Callback(hObject, eventdata, handles)  
global Current_Balance
(...)
%Press buttonB to play coin game
function buttonB_Callback(hObject, eventdata, handles)  
global Current_Balance
(...)
%Press button C to show the result  
function buttonC_Callback(hObject, eventdata, handles)
global Current_Balance
set (handles.text1,'string',Current_Balance)

It worked this time. Thanks a lot.

[Stephen23]

@Nguyen Quang: declaring the variable as global is not a good solution, because using globals is a bad way to write code. Read the links that Jan Simon gave you, they describe much better solutions.

You should avoid globals:

https://www.mathworks.com/matlabcentral/answers/332403-global-variables-in-a-guide-gui

https://www.mathworks.com/matlabcentral/answers/332491-how-to-fix-this-error-attempt-to-reference-field-of-non-structure-array