How do I use an array of files?

I have this code below which I am trying to make an array of files to use in a loop so I don't have to rewrite the same code over and over again, but when I use this method the array only pulls the first letter of the file name making it impossible to access that file. The fname array is the one I am trying to specify, but when I make it a string array it does not recognize the names as a file. Thanks in advance.

   L = 50.8; %Support Span as measured in mm.
  b = 24.75; %Width of rock as measured in mm.
  d = 10.2; %Thickness of rock as measured in mm.

fname = ['Specimen_RawData_1.xls','Specimen_RawData_2.xls',...
    'Specimen_RawData_3.xls','Specimen_RawData_4.xls',...
    'Specimen_RawData_5.xls','Specimen_RawData_6.xls',...
    'Specimen_RawData_7.xls','Specimen_RawData_8.xls',...
    'Specimen_RawData_9.xls','Specimen_RawData_10.xls',...
    'Specimen_RawData_11.xls','Specimen_RawData_12.xls',...
    'Specimen_RawData_13.xls','Specimen_RawData_14.xls',...
    'Specimen_RawData_15.xls','Specimen_RawData_16.xls',...
    'Specimen_RawData_17.xls','Specimen_RawData_18.xls',...
    'Specimen_RawData_19.xls','Specimen_RawData_20.xls',...
    'Specimen_RawData_21.xls','Specimen_RawData_22.xls',...
    'Specimen_RawData_23.xls','Specimen_RawData_24.xls',...
    'Specimen_RawData_25.xls'];

for i = 1:25

      a = xlsread(fname(i));

      x = a(:,3);
      y = a(:,4);

      [ra,ca,va] = find(y > i);

      ta = ra(1);

      [rb,cb,vb] = find(y > i - 10);

      tb = rb(1);

      m = ((y(ta)-y(tb))/(x(ta)-x(tb)))/1e3

      E = ((L^3)*m)/(4*b*d^3)

      n = i;

      plot(n,E,'*')

end

Answer 1

[Oleg Komarov]

Implement these changes:

% Fname as a cell array of strings
fname = {'Specimen_RawData_1.xls',... 
         ...} 

% note the curly brackets
a = xlsread(fname{i});

[Daniel Jednorozec]

Wow, thank you so much. What a difference brackets make.

Answer 2

[Matt Tearle]

Strings in MATLAB are treated as a matrix of characters. Hence,

fname = ['Specimen_RawData_1.xls','Specimen_RawData_2.xls']

will make a 1-by-44 character array containing the string 'Specimen_RawData_1.xlsSpecimen_RawData_2.xls' (because you concatenated the two strings (char arrays) together horizontally).

So first fix is to concatenate them vertically into a matrix of characters:

fname = ['Specimen_RawData_1.xls';'Specimen_RawData_2.xls']

(Note the ; instead of ,). Now you have a matrix of two rows, one per string. To index into each filename in the loop, then, use

a = xlsread(fname(i,:));

Now, if your filenames have different lengths, you will not be able to concatenate vertically (all rows of a matrix must have the same number of columns).

So another approach is to use a cell array of strings:

fname = {'Specimen_RawData_1.xls','Specimen_RawData_2.xls'}

Then use cell indexing in the loop:

a = xlsread(fname{i});

Finally, you may want to investigate the functions ls and dir. You may also want the cellstr function for converting a char array to a cell array of strings.