MATLAB: How to plot a function which depends on a changing variable

oscillationplotspringvariable

So I have to plot the movement of a spring once let go for -2<t<20 given yo=5(distance the spring is stretched initially), w=5(angular frequency), k=0.1/s. It has to be done using a for loop and if statements.
I am new to matlab so I don't know what to do from here. Thank you.
Here's the code I have:
    t = -2;    yo = 5;    w = 5;    k = 0.1;    for t = -2:20      if t < 0           y = -yo;      elseif t < 10          y = -yo*(cos(w*t));      else          y = -yo*(cos(w*t))*exp(-k*(t-10));      end      t = t + 0.1;    end

t_all = -2:0.1:20;y = zeros(1,length(t_all));for i = 1:length(t_all)   t = t_all(i);   y(i) = ...endplot(t_all,y)