Your script overwrites x,y,z for each iteration. You need to assign vectors of appropriate length to x,y,z , (preallocate) before running the loop. Try
t=0;
ix=0;
v=pi/10;
r=6;
dt=0.1;
w=v/r;
x = nan(round(100/dt),1);
y = x;
z = x;
while t<100
ix = ix + 1;
t=t+dt;
x(ix)=r*sin(theta-w*t);
y(ix)=r*cos(theta-w*t);
z(ix)=sqrt(10^2-x^2-y^2);
end
Just to learn how to use a loop, despite it is not neccessary in your example.
