Numbering variables like that is not a good way to write MATLAB code. You could do that, but you force yourself into writing slow, complex, obfuscated, buggy code that is hard to debug. That approach is not recommended.
The simple, efficient, recommended approach is to use indexing, e.g. with a cell array:
C = {'428a2f98d728ae22';
'7137449123ef65cd';
'b5c0fbcfec4d3b2f';
'e9b5dba58189dbbc';
'3956c25bf348b538';
'59f111f1b605d019';
'923f82a4af194f9b';
'ab1c5ed5da6d8118';
'd807aa98a3030242';
'12835b0145706fbe';
'243185be4ee4b28c';
'550c7dc3d5ffb4e2';
'72be5d74f27b896f';
'80deb1fe3b1696b1';
'9bdc06a725c71235';
'c19bf174cf692694'};
N = numel(C);
D = cell(N,1);
for k = 1:N
D{k} = fn_hex2bin(C{k});
end
