clear
format compact

% have slightly different n at every run (to avoid precompilation?)
n = 100000 + randi([0 10])

% loop without preallocation
tic();
for i = 1:n
    x(i) = i;
end
t_wo = toc()

% loop with preallocation
y = zeros(1, n); % preallocate a row vector
tic();
for i = 1:n
    y(i) = i;
end
t_w = toc()

% Speedup factor
t_wo/t_w