Your code does almost work. Start at 1 and stop at 100-8+1. Note that 8 elements have the indices i:i+7, not i:i+8.
w = 8;
MA8 = zeros(1, 100 - w + 1); % Pre-allocation
for k = 1:100 - w + 1
MA8(k) = sum(C(k:(k+w-1))) / 8;
end
The output must be shorter than the input. The pre-allocation avoids to let the array grow iteratively, because this is very expensive. I use "k" as loop counter instead of "i" to reduce the danger of confusions with the imaginary unit "i". This is recommended in the documentation (see also: https://www.mathworks.com/matlabcentral/answers/46648-using-i-and-j-as-variables)
Do you know the movmean command?
MA8 = movmean(C, 8, 'Endpoints', 'discard');
Much faster and easier than writing your own loop.
