Unit step function - Explain this 10 line code?

i Folks,

I have difficulty understanding what is happening with this code. It is meant to simulate the unit step function

(t-a)=1 for t>a and (t-a)=0 for t<a

The resulting output is vector of 0's and 1's when its inside another function. However, when I extract the function for simplicity to show here, it just calculates a bunch of 1's. In either case, i dont understand the 3rd last line...

function y = h(t)
t = linspace(0,36*pi,2^15)';
    y = zeros(size(t));
    for k = 1:length(t)
        if t(k)>0
            y(k) = 1;
        else
            y(k) = 0;
        end
    end

function y = U(t,i,N,Tc)

      y = 0;
  N=1;
  Tc=6.28;
      for i=1:N
      for n=1:100
          y = y + h(t-(((n-1)*N+i-1)/N)*Tc) - h(t-(((n-1)*N+i)/N)*Tc);
      end
      end

Thanks