how do i debug my program

i have here a picture of the problam and also i attached here the code which is going wrong. what i am trying to do is to update the info in the vector integ(i) by summerizing each cell with the integral's calculation. for this iam writing integ(i)= int(...) + integ(i) however for some reson, as you can see in the picture below (click on it) i highlight in red that the values are 0 and i don't understand why it is not being updated with new values. please help me to correct my code.

l=1;
h=l/10;
n=round(l/h); 
syms t j
  K(t)=exp(-t);
  F(t)=t;
   integrand(t,j) = K(t-j)*F(j);
   U(t)=1 - int(integrand(t,j),j,0,t);
   Uexact=zeros(1,n+3);
   Utest=zeros(1,n+3);
   integ=zeros(1,n+3);
   Udiff=zeros(1,n+3);
   LOGtest=zeros(1,n+3);
   ERRORord=zeros(1,n+3);
   for i=2:n+1
       for m=1:i
       integ(i)=int(K((i-1)*h-j)*(1/h)*((F(m*h)-F((m-1)*h))*j+h*(i*F((m-1)*h-(m-1)*F(m*h)))),j,(m-1)*h,(m*h))+integ(i);
       end