MATLAB: Ode45 events using problem

Question

[T,Z] = ode45(@bouncing, [0 12], [100 0],'tspan','options','events');
options = odeset('events');
events(t,z) = [y(1)-10,1,-1]
value = y(1)-10;
isterminal = 1;
direction = -1;
axis([-5 5 0 120])
a = 0;
y = Z(:,1);
while a < 69
  viscircles([0,y(1+a)],10,'Linewidth',10');
  pause(0.1);
  cla;
  a = a+1;
end

Answer 1

events = @(t,y) [y(1)-10, 1, -1];
options = odeset('events', events);
[T,Z] = ode45(@bouncing, [0 12], [100 0], options);
axis([-5 5 0 120])
y = Z(:,1);
for a = 1 : 69
  viscircles([0,y(a)],10,'Linewidth',10');
  pause(0.1);
  cla;
end

However, I do not see any reason to assume you will get at least 69 results. It would make more sense to use length(y) instead of 69.