"While" this does not answer your question, I would not use a while loop at all. Learn to use MATLAB as it is designed.
B is the same length as A. Note that A(1) will never be greater than the preceding element, since there is no preceding element.
Could you use a while loop? Yes. A for loop would make more sense as a loop here, since you want to test EVERY pair of elements.
B(ind) = A(ind) > A(ind-1);
Same result as the single statement, but a loop.
CAN you use a while loop? Well, yes. Learn when to use one type of loop over another when you REALLY need to use a loop. A while loop is good when you don't know how often the loop will run. A for loop is right when you have a known, fixed number of iterations.