how to plot a graph from a data file

I've data input file name "data.txt" formed:

"Measured Data
23-Dec-2011
t,f(t) 
1,12.9
2,11.3
3,10.6
4,11.2
5,10.9
6,7.5"

but i don't know how to plot this file,i got wrong graph,here is code:

filename = input (' Enter your file name  : ','s');
fid = fopen(filename,'r');
  if fid == -1
      disp('File open not successful')
  else

      while feof(fid) ==0
          aline = fgetl (fid);
         [num1, num2] = strtok(aline);

          a = str2num (num1);
          b = str2num(num2);

          plot(a,b,'ob');

          hold on

      end

      closeresult = fclose(fid);
      if closeresult == 0
          disp ('File close successful')
      else
          disp ('File close not successful')
      end
  end

   * Error is :*
  ??? Error using ==> plot
  Vectors must be the same lengths.

Answer 1

[Walter Roberson]

Please have a look at my response in http://www.mathworks.com/matlabcentral/answers/21210-arrarys