I want to plot z such that z(:,1)= [0;1]; but how do I implement that in this code

close all;
dt = 0.1;%time step
u1=1;
u2=2;
c = u2-u1;
u = sign(u2-u1);
z=u*c;




k=0.12;
m=2.21;%initial parameters

v=1;
a=1.4;

tend=1000;

t=0;
i=1

while (t < tend-2*dt & i<t)
    vh=v(i)-dt*k*z(1,i)/ (2*m);
    z(2,i) = z(1,i)+ dt*vh;
    %a(i+1)= -k*z(i)/2;
    v(i+1)= vh-dt*k*z(2,i)/ (2*m);% + dt*a(i+1)/2;
    i = i+1;
    t = t + dt
end
plot(z);

[Walter Roberson]

How does this differ from https://www.mathworks.com/matlabcentral/answers/469021-how-can-i-put-the-value-of-z-in-a-matrix-and-later-call-it-as-z-1-i-and-z-2-i-in-the-while-loop ?