You're overwriting all your variables inside the loop so you'd only see the result of the last iteration. You'd need to use arrays to store output of each iteration.
%preallocate
N = zeros(1,11);
SNR_db=0:10;
%other variables as well
for k = 1:11
N(k)=((E)/(10^(SNR_db(k)/10)));
...
end
or use matlab wisely without a loop,
SNR_db = 0:10;
N=E./(10.^(SNR_db./10));
%and so on
