Stuck in infinite loop?

Question

Scott J 2015-12-6

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/259138-stuck-in-infinite-loop

评论： Image Analyst 2019-11-20

Probably doing something stupid..

question = input('Enter a question about volume: ','s');
checkExit = 'exit';
exit = strfind(question,checkExit);
while(length(exit)==0)
ifCube = 'cube';
cube = strfind(question,ifCube);
if(length(cube)==0)
    display('you did not specify the shape');
    %the word cube isn't in the sentence
else
    posH = 'height of';
    Index = strfind(question, posH);
    height = sscanf(question(Index(1) + length(posH):end), '%d', 1);
    volCube = height * height * height
end
ifCyl = 'cylinder';
cylinder = strfind(question,ifCyl);
if(length(cylinder)==0)
    %the word cylinder isn't in the sentence
else
    posH = 'height of';
    Index = strfind(question, posH);
    height = sscanf(question(Index(1) + length(posH):end), '%d', 1);
      posR = 'radius of';
      Index2 = strfind(question, posR);
      radius = sscanf(question(Index2(1) + length(posR):end), '%d', 1);
      volCyl = 2*pi*radius*height
  end
ifCone = 'cone';
cone = strfind(question,ifCone);
if(length(cone)==0)
    %the word cone is not in the sentence
else
    posH = 'height of';
    Index = strfind(question, posH);
    height = sscanf(question(Index(1) + length(posH):end), '%d', 1);
    posR = 'radius of';
    Index2 = strfind(question, posR);
    radius = sscanf(question(Index2(1) + length(posR):end), '%d', 1);
    volCone = pi*((radius)^2)*(height/3)
end
ifSphere = 'sphere';
sphere = strfind(question,ifSphere);
if(length(sphere)==0)
    %the word sphere is not in the sentence
else
     posR = 'radius of';
     Index2 = strfind(question, posR);
     radius = sscanf(question(Index2(1) + length(posR):end), '%d', 1);
     volSphere = (4/3)*pi*(radius)^3
end 
end

I want to keep asking the user to enter a question about volume until the say 'exit'. However, I don't know how to keep myself from getting stuck in while loop, if I set exit = 1 in each of the if statements it breaks the out of the while loop obviously but I want to continuously ask the user questions. I'm stumped, and a point in the right direction would be very helpful.

Thank you.

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Answer 1

Image Analyst 2015-12-7

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https://ww2.mathworks.cn/matlabcentral/answers/259138-stuck-in-infinite-loop#answer_202400

在 MATLAB Online 中打开

"exit" is a built in function that terminates a MATLAB program. Don't use that name, obviously, or any other name of any other built-in function.

Put the strfind inside the while test and inside a call to isempty(), so make those two lines into this single line.

while isempty(strfind(question,checkExit))

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Scott J 2015-12-7

编辑：Scott J 2015-12-7

在 MATLAB Online 中打开

Thank you a lot, I'll start doing that now. What I did to "fix" it before you commented is that I put question into the cube if statement, but then that really only fixed the problem if the user starts with a question about a volume of a cube with height = x. If they ask about any other shapes, it just displays their question until they ask about a cube and then works correctly. How can I fix that?

    while(length(exit)==0) %while isempty(strfind(question,checkExit)==0)
    ifCube = 'cube';
    cube = strfind(question,ifCube);
    if(length(cube)==0)
        %the word cube isn't in the sentence
        question = input('Enter a question about volume: ','s');
        %repeats question
    checkExit = 'exit';
    exit = strfind(question,checkExit);
    else
        posH = 'height of';
        Index = strfind(question, posH);
        height = sscanf(question(Index(1) + length(posH):end), '%d', 1);
        volCube = height * height * height
        question = input('Enter a question about volume: ','s');
        %repeats question
    checkExit = 'exit';
    exit = strfind(question,checkExit);
    end

Image Analyst 2015-12-7

在 MATLAB Online 中打开

Try it like this instead:

% Ask user for two responses.
defaultValue = {'cube', '42'};
titleBar = 'Enter values';
userPrompt = {'Enter question about volume : ', 'Enter height: '};
loopCounter = 1;
maxNumberOfLoops = 8; % Failsafe - whatever you want.
while loopCounter < maxNumberOfLoops
  caUserInput = inputdlg(userPrompt, titleBar, 1, defaultValue);
  if isempty(caUserInput),break,end; % Bail out if they clicked Cancel.
  % Convert to floating point from string.
  usersValue1 = caUserInput{1}
  % Bail out if they typed quit or exit also.
  if strcmpi(usersValue1, 'quit') || strcmpi(usersValue1, 'exit')
    break;
  end
  usersValue2 = str2double(caUserInput{2})
  % Check for a valid number.
  if isnan(usersValue2)
    % They didn't enter a number.
    % They clicked Cancel, or entered a character, symbols, or something else not allowed.
    % Convert the default from a string and stick that into usersValue1.
    usersValue1 = str2double(defaultValue{2});
    message = sprintf('I said it had to be a number.\nI will use %.2f and continue.', usersValue1);
    uiwait(warndlg(message));
  end
  height = usersValue2;
  % Now computer volume
  volCube = height * height * height;
  % Tell user what it is:
  promptMessage = sprintf('The volume = %f', volCube);
  titleBarCaption = 'Continue?';
  buttonText = questdlg(promptMessage, titleBarCaption, 'Continue', 'Quit', 'Continue');
  if strcmpi(buttonText, 'Quit')
    break;
  end  
end

NN 2019-11-20

Hi Sir,

I am using if conditions in simulink with logical operators and i experince same problem , matlab hangs after running the simulation.I doubt if the loop goes to inifinity and if so how can i correct it in simulink .My model is a power system model and if condition has to check net power at ac grid continuosly during simulation time.can i add any other block in simulink itself to solve this isissue or need to write program

Image Analyst 2019-11-20

Use a failsafe like I showed: a check on the number of iterations so you don't get into an infinite loop.

Attach your code if you need more help. But I don't have Simulink so I can only advise on MATLAB code.

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