What is the best way to solve difference equations using matlab without using filter command?

We're assigned to solve for a 2nd order difference equations using matlab but without using the built in function filter and filtic. The problem doesn't necessarily stated the inputs rather than it must be a script file.

function lccde

clc

xn= input('Coefficient of y(n): ');

xn1 = input('Coefficient of y(n-1): ');

xn2 = input('Coefficient of y(n-2): ');

yn = input('Coefficient of x(n): ');

yn1 = input('Coefficient of x(n-1): ');

yn2 = input('Coefficient of x(n-2): ');

X = input('Input sequence x(n): ');

xic1 = input('Initial condition at y(-1): ');

xic2 = input('Initial condition at y(-2): ');

nf = input('How many terms?: ');

nc=1/xn;

for n=3:nf

      n0=1:3;
      if (n-n0==2)
          Y(0)=nc*(xn1*xic1+xn2*xic2+yn*X(n-3)+yn1*X(n-2)+yn2*x(n-1))
      elseif (n-n0==1)
          Y(1)=nc*(xn1*y(0)+xn2*xic1+yn*X(n-3)+yn1*X(n-2)+yn2*X(n-1))
      else (n-n0==0)
          Y(n)=0;
          Y(n)=nc*(xn1*y(n-1)+xn2*y(n-2)+yn*X(n-3)+yn1*X(n-2)+yn2*X(n-1))
      end
  end

[Jan]

What is your question?