This is a working for-loop, which prints out something that resembles your goal:
a = input('Enter the Array:');
for i = 1:length(a)
v = a(i) ; % get the i-th element of a
if v > 0
fprintf('v>0',i)
elseif v < 0
fprintf('v<0',i)
else
fprintf('v=0',i)
end
end
However, the next step is to learn to do this in a matlab-like way
V = input('Enter the Array:');
disp('V < 0') ;
idx = find(V<0) ; % all at once
disp(idx) ;
