well first you'll want to get away from generating variables in that fashion as you'll basically have A400 or more which is hard to keep track of. instead of manually you can use the function dir() which can poll a file for the files in a folder. (in combination with uigetdir/uigetfile you can navigate to another folder without coding in the file locations.)
example:
xlfiles = dir('*.xlsx')
for ind = 1:numel(xlfiles)
A(:,:,ind) = xlsread(xlfiles(ind).name);
end
if they are at different sizes you can use structs which i think goes like this:
data = struct('A',[])
for ind = 1:numel(xlfiles)
data(ind).A = xlsread(xlfiles(ind).name);
end
or alternatively put it into a cell array
