Think we need more specific example of what blah... is and what it is that you're trying to repeat.
As your code snippet is written there's nothing that wouldn't work(+) but it's not clear that it's of much use, either...
(+) "Work" as in run without a compilation error. What the result would be compared to what would be wanted is something else again. Of course, one would normally preallocate loop here before the for construct as
loop=zeros(100,1); % explicitly allocate array
or equivalently,
loop(100,1)=0; % automagically allocates array
