saving values in an array from an iteration

can someone help me i have this code it takes a number of images (200) each 20 images are from 1 folder so that 10 folders.

im trying to take the mean and standard deviation of each image and store them in an array, i already have an array 'F' that takes the mean and standard deviation as attributes and i created another area with 2 rows and 200 columns to fit the mean and standard deviation of each image in each column. how can i do that ?

this is my code :

for i = 1:10                                 %read folder 10 times
    fname = strcat('C:\Users\Basma\Desktop\projectpartialdb\' , num2str(i))     
    dir(fname)
        for j= 1:20                          % read all 20 images in each folder
       imname = strcat(fname , '\' , num2str(j), '.png')
       im=imread(imname);
       im=im2bw(im);
       F=FeatureStatistical(im)    % an array that takes the mean and standard deviation as attributes
        end
end

this is what i want to do i want to iterate on all of the 200 images and take their mean and standard deviation and store them in array A. where each column represent an image.

 for i = 1:200
 A = [1:200;1:200];
F=FeatureStatistical(im)
%it says here that i can't use i as an array element 
      A(1,i) = F(m) ; 
      A(2,i) = F(s) ;
end