How to put all the values of a for loop in a vector?

I want D_N to get another value in each loop and then put that value in a vector, T amount of times. Basically, I want to be able to go through the script an T amount of times and each time D_N will get another value and then put it into a vector. How do I do this?

clear
clc

N = 100;
M = 2000;
B = zeros(M,N);

for m=1:M

    x_t(1) = 0;
    for n = 1:N

        A = sign(randn);
        x_t(n+1) = x_t(n) + A;
        B(m,n) = x_t(n); 
    end
        hold on

end

C = B(:,end);
D = C.^2;
D_N = sqrt(mean((D)))