Using Switch/Case to assign values

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Poseidon 2023-4-20

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评论： Cris LaPierre 2023-4-20

Hi

I am trying to use switch/case like below but when I run it, says eq is unrecognised variable or function. This is for an app.

switch app.SelectEvaporatorTypeDropDown.Value

case 'Forced Circlation (pumped)'

eq(1)=1;

case 'Falling Film'

eq(1)=2;

case 'Agitated Film (scraped wall)'

eq(1)=3;

case 'Short Tube'

eq(1)=4;

case 'Long Tube'

eq(1)=5

end

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DGM 2023-4-20

I don't see any way that the given code would ever produce that specific error. While eq() is a builtin function, and it's probably a bad idea to be naming your variables after functions, it's not apparent to me how that would be causing this specific error either.

Of course, you didn't include the entire error message backtrace, so it's not clear that this chunk of code is even part of the problem.

Fangjun Jiang 2023-4-20

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Although not recommended, your code does not have error here.

"eq" is a function. use some other variable name, e.g. Myeq
Before this code, pre-allocate the variable and value, Myeq=1;

app.SelectEvaporatorTypeDropDown.Value='Forced Circlation (pumped)';
switch app.SelectEvaporatorTypeDropDown.Value
    case 'Forced Circlation (pumped)'
        eq(1)=1 
    case 'Falling Film'
        eq(1)=2;
    case 'Agitated Film (scraped wall)'
        eq(1)=3;
    case 'Short Tube'
        eq(1)=4;
    case 'Long Tube'
        eq(1)=5
end
eq = 1

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Answer 1

Cris LaPierre 2023-4-20

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https://ww2.mathworks.cn/matlabcentral/answers/1950558-using-switch-case-to-assign-values#answer_1219848

编辑：Cris LaPierre 2023-4-20

I suspect the error is not occuring in the lines of code you have shared, but later on in another function when you try to use eq. Keep in mind variable scope. All your code in an app is inside functions. Once that function completes, its workspace is cleared.

If you want to share data between functions in your app, you must add the variable as a property of the app. See here: https://www.mathworks.com/help/matlab/creating_guis/share-data-across-callbacks-in-app-designer.html

You then access it by prepending with the property name with your app object name, like so: app.eq

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Poseidon 2023-4-20

在 MATLAB Online 中打开

  
    properties (Access = private)
        Myeq(1,:) % Equipment
    end
    
    % Callbacks that handle component events
    methods (Access = private)
        % Value changed function: Button
        function ButtonValueChanged(app, event)
            value = app.Button.Value;
                Kvalues=readtable('Kvalues.txt');
                
            
             
                switch app.SelectEvaporatorTypeDropDown.Value
                    case 'Forced Circlation (pumped)'
                        app.Myeq(1)=1; 
                    case 'Falling Film'
                        app.Myeq(1)=2;
                    case 'Agitated Film (scraped wall)'
                        app.Myeq(1)=3;
                    case 'Short Tube'
                        app.Myeq(1)=4;
                    case 'Long Tube'
                        app.Myeq(1)=5;
                end
                switch app.SelectCondenserTypeDropDown
                    case 'Forced Circlation (pumped)'
                        app.Myeq(2)=1; 
                    case 'Falling Film'
                        app.Myeq(2)=2;
                    case 'Agitated Film (scraped wall)'
                        app.Myeq(2)=3;
                    case 'Short Tube'
                        app.Myeq(2)=4;
                    case 'Long Tube'
                        app.Myeq(2)=5;
                end
                switch app.SelectPumpTypeDropDown.Value
                    case 'Reciprocating'
                        app.Myeq(3)=6; 
                    case 'Positive Displacement'
                        app.Myeq(3)=7;
                    case 'Centrifugal'
                        app.Myeq(3)=8;
                end
                switch app.SelectTurbineTypeDropDown.Value
                    case 'Axial Gas Turbine'
                        app.Myeq(4)=9;
                    case 'Radial Gas/Liquid Expanders'
                        app.Myeq(4)=10;
                end
                
                Evap=app.Myeq(1);
                Cond=app.Myeq(2);
                Pump=app.Myeq(3);
                Turb=app.Myeq(4);
               app.EvapEditField.Value=Evap;
               app.CondEditField.Value=Cond;
               app.PumpEditField.Value=Pump;
               app.TurbEditField.Value=Turb;
        end
    end

Ok so I tried this. Thinking I am using properties in the wrong way though. Getting this error:

Index exceeds the number of array elements (0).

Error in test/ButtonValueChanged (line 80)

Evap=app.Myeq(1);

Error using matlab.ui.control.internal.controller.ComponentController/executeUserCallback (line 429)

Error while evaluating StateButton PrivateValueChangedFcn.

Poseidon 2023-4-20

编辑：Poseidon 2023-4-20

Thank you this helped.

There were actually other mistakes I did that was basically causing the problems (messed up the names of the cases and similar mistakes where app and code weren't matching which was causing cases to evaluate false)

Cris LaPierre 2023-4-20

在 MATLAB Online 中打开

Just an additional note that you can also preallocate your property this way:

properties (Access = private)
    Myeq = zeros(1,4); % Description
end

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