While loop runs inconsistently, most often generating a vertcat error.

Hey everyone, any help or tips y'all could give me would be greatly appreciated. I'm running a nested loop code to produce a 3D plot containing multiple lines generated from the nested portion of the code. The z coordinate is constant for each line, and only changes between lines. The issue I'm running into is that when I run the code I get a vertcat error more often than not, due to the z array being 1x19 double, while the x and y arrays are 1x18 double. I understand why the vertcat error causes the code to stop, but I don't understand why the vertcat error is being created in the first place. Below is a picture from a successful run to show the desired result, as well as my code. Any clue what's going wrong? I assume it's some issue with how I'm incrementing the value of z. I've tried relocating the incrementing line higher in the code since I thought maybe it was generating a final z value after x and y had finished, causing the z array to have one value more than the other two. However, that hasn't removed the error, and if that was the case then I would think the code would have the vertcat error every time it ran instead of only sometimes.

clc
clear all
z = 0; %initializing starting z value
k = 1;
while z <= 0.16
    x = 0+(4-0).*rand(1,1); %initializing starting x value
    L = .25; %0.25mm segment length between nodes
    y = 0; %initializing starting y value
    i = 1;
    while y<=4
        x(i+1) = x(i) + (.25*sind(-40+(40+40).*rand(1,1)));
        y(i+1) = y(i) + (.25*cosd(-40+(40+40).*rand(1,1)));
        z(i+1) = z(i);
        i = i + 1;
    end
    xyz{k} = [x;y;z];
    plot3(x,y,z,'o')
    axis([-1 5 -1 5 0 0.16])
    hold on
    fnplt(cscvn(xyz{k}(:,[1:end])),'r',2)
    z = z+0.01;
    k = k+1;
  
end
hold off

Answer 1

[Sean Clifton]

Nevermind, I embarrasingly missed the easy solution here. I switched from a While loop to a for loop to increment the z values. Below's the code that ended up solving the problem:

clc
clear all
z = 0; %initializing starting z value
k = 1;
for z = 0:0.01:0.16
    x = 0+(4-0).*rand(1,1); %initializing starting x value
    L = .25; %0.25mm segment length between nodes
    y = 0; %initializing starting y value
    i = 1;
    while y<=4
        x(i+1) = x(i) + (.25*sind(-40+(40+40).*rand(1,1)));
        y(i+1) = y(i) + (.25*cosd(-40+(40+40).*rand(1,1)));
        z(i+1) = z(i);
        i = i + 1;
    end
    xyz{k} = [x;y;z];
    plot3(x,y,z,'o')
    axis([-1 5 -1 5 0 0.16])
    hold on
    fnplt(cscvn(xyz{k}(:,[1:end])),'r',2)
    k = k+1;
end
hold off