A loop is completely unnecessary:
B = A;
B(B>360) = B(B>360) - 360;
Using a loop, this would have been the proper syntax:
B = zeros(size(A)); %always preallocate
for idx = 1 : numel(A) %your loop indexing was completely wrong
if A(idx) < 360
B(idx) = A(idx); %and of course, you must use the index somewhere
else %no need for elseif A(idx)>=360, if the 1st condition wasn't true, then the other one obviously is
B(idx) = A(idx) - 360;
end
end
Note that if all you want to do is make sure that values in B are between 0 and 360, then:
B = mod(A, 360);
is even simpler.
