Creating Library with App Designer

value = app.ISBNEditField.Value;
            ISBN=app.ISBNEditField.Value;
            BOOKS=app.BOOKSListBox.Value;
            GetBook=app.GetBookButton;
            Information=app.InformationTextArea;
            GetBook=[1234 1235 1236 1237];
            Books=input('Anna Karenina,Les Miserables,War and Peace,Of Mice and Man','s');
            function output=Library
               if a == 1234
                  Information = 'Anna Karena';
              elseif a == 1235
                   Information = 'Les Miserables';
              elseif a == 1236
                   Information = 'War and Peace';
              elseif a == 1237
                   Information = 'Of Mice and Men';
                else
                   Information = 'not available';
            end
           app.InformationTextAreaLabel.Text = 'not available right now';
          for i = 1 : length(app.BOOKSlist.Items)
            if ISBN == app.BOOKSlist.Items(i)
              app.InformationTextAreaLabel.Text = string(i);
            break;
            end
          end
            end
            
        for app.GetBookButton=1234
            app.InformationTextArea.Author=='Tolstoy';
            app.InformationTextArea.Pages=='1000';
            
            
        if  app.GetBookButton==1235  
            app.InformationTextArea.Author=='Hugo';
            app.InformationTextArea.Pages=='416';
          
            
        for app.GetBookButton==1236
            app.InformationTextArea.Author=='Tolstoy';
            app.InformationTextArea.Pages='516';
         
        
        for app.GetBookButton=1237
            app.InformationTextArea.Author=='John Steinbeck';
            app.InformationTextArea.Pages=='187';
           
        end
        end

It keeps giving me this error:

Error using Library
Error: File: Library.mlapp Line: 53 Column: 16
Unexpected MATLAB operator.

[Adam Danz]

You've defined a function Library with no inputs nor outputs. Which line is creating the error?

[Esin Derin]

app.InformationTextArea.Author=='Tolstoy';

app.InformationTextArea.Pages=='1000';

With equal signs.

[Esin Derin]

Defined a function with two variables but this isn't working either.No error,just not working.

function output = my_output(x,y)
           ISBN=app.ISBNEditField.Value;
            BOOKS=app.BOOKSListBox.Value;
% it affect app getbookbutton to getbookbutton
            GetBook=app.GetBookButton;
            Information=app.InformationTextAreaLabel.Text;
            GetBook=[1234, 1235 ,1236, 1237];
           % this function output the information of book
           
% count number of enter books
          for i = 1 : length(app.BOOKSlist.Items)
            if ISBN == app.BOOKSlist.Items(i)
              app.InformationTextAreaLabel.Text = string(i);
            break;
            end
       
           
        if app.GetBookButton==1234
           app.InformationTextArea.Author='Tolstoy';
            app.InformationTextArea.Pages='1000';
           output(app.InformationTextArea.Author,app.InformationTextArea.Pages)
           
        elseif  app.GetBookButton==1235  
            app.InformationTextArea.Author='Hugo';
            app.InformationTextArea.Pages='416';
output(app.InformationTextArea.Author,app.InformationTextArea.Pages)
         
           
        elseif app.GetBookButton==1236
            app.InformationTextArea.Author='Tolstoy';
            app.InformationTextArea.Pages='516';
output(app.InformationTextArea.Author,app.InformationTextArea.Pages)
         
       
        elseif app.GetBookButton==1237
            app.InformationTextArea.Author='John Steinbeck';
            app.InformationTextArea.Pages='187';
output(app.InformationTextArea.Author,app.InformationTextArea.Pages)
elseif  output('not information for author','not information')
        end
       
    end

Answer 1

[Adam Danz]

When comparing strings or char arrays, use strcmp() instead of A==B. Also, to combine conditions, use && as shown below.

        if  app.GetBookButton==1235  && ...
            strcmp(app.InformationTextArea.Author, 'Hugo') &&...
            strcmp(app.InformationTextArea.Pages, '416')

strcmp() is case-sensitive. For case insensivitity, use strcmpi().

[Esin Derin]

It gives error in methods.

[Esin Derin]

  function output = my_output(x,y)
           ISBN=app.ISBNEditField.Value;
            BOOKS=app.BOOKSListBox.Value;
% it affect app getbookbutton to getbookbutton
            GetBook=app.GetBookButton;
            Information=app.InformationTextAreaLabel.Text;
            GetBook=[1234, 1235 ,1236, 1237];
           % this function output the information of book
           
% count number of enter books
          for i = 1 : length(app.BOOKSlist.Items)
            if ISBN == app.BOOKSlist.Items(i)
              app.InformationTextAreaLabel.Text = string(i);
            break;
            end
       
           
        if app.GetBookButton==1234 
           strcmp(app.InformationTextArea.Author,'Tolstoy') 
            strcmp(app.InformationTextArea.Pages,'1000')
           output(app.InformationTextArea.Author,app.InformationTextArea.Pages)
           
        elseif  app.GetBookButton==1235 
            strcmp(app.InformationTextArea.Author,'Hugo') 
            strcmp(app.InformationTextArea.Pages,'416')
output(app.InformationTextArea.Author,app.InformationTextArea.Pages)
         
           
        elseif app.GetBookButton==1236 
           strcmp(app.InformationTextArea.Author,'Tolstoy') 
           strcmp(app.InformationTextArea.Pages,'516')
output(app.InformationTextArea.Author,app.InformationTextArea.Pages)
         
       
        elseif app.GetBookButton==1237 
            strcmp(app.InformationTextArea.Author,'John Steinbeck') 
            strcmp(app.InformationTextArea.Pages,'187')
output(app.InformationTextArea.Author,app.InformationTextArea.Pages)
elseif  output('not information for author','not information')
        end
       
          end
             end
            

[Adam Danz]

What is the entire copy-pasted error message?

What are the values of the variables producing the error?