You should preallocate the `cs` cell array:

    [v,x] = find(diff(a)>1); %find "jumps"
    xx = [0 x length(a)];
    cs = cell(length(a)+1,1);
    for ii = 1:length(xx)-1
       cs{ii} = a(xx(ii)+1:xx(ii+1));
    end

Style comments:

 - Try to keep consistent formatting, either put spaces around all equal signs, or around none.

 - Terminate statements with a semicolon to prevent your function producing output to the command window.