I want to find particular values of t at which y becomes 2 (by writing some commands in code itself). Can I extract such values of t as a vector?

 I am requesting you for one more favor.
 C=1;
  for j=2:N
      t(j)=t(j-1)+dt;
      y(j)=y(j-1)+dt*sin(t(j-1))+C;
  end
  zci = @(v) find(v(:).*circshift(v(:), [-1 0]) <= 0);  
  idx_2 = zci(y - 2);                                                                   
  for k = 1:numel(idx_2)
      t2(k) = interp1(y(idx_2(k)+[-1 1]), t(idx_2(k)+[-1 1]), 2, 'linear','extrap');   
  end
  % I want to use C=2 at t=t2 otherwise C=1 (continue with upper loop of j).
  % Which probably means I can terminate upper j loop at the end of code only. 
% If I repeat j loop like below then there is no calculation for C=1 
% for t not equal to t2. Please suggest me.
  for j=2:N
      t(j)=t(j-1)+dt;
      for k=1:numel(idx_2)
          if t(j)==t2(k)
              C=2;
            y(j)=y(j-1)+dt*sin(t(j-1))+C;
          end
      end
  end

% Sorry for confusion. I am trying to use t2 values for applying
 % if condition on C. If t=t2 then C=2 otherwise C=1. This is my
 % running code. Main problem here is for values of t other than 
% t2, y(j) is calculated using second (last) j loop not using
% first (uppermost) j loop. Any hints?

N=2000;  % Number of time stpes
dt=0.05;  %Time step
%Initialize
 y=zeros(N,1); 
 t=zeros(N,1);
%Initial values
t(1)=0;
y(1)=1;
 C=1;
    for j=2:N
          t(j)=t(j-1)+dt;
    y(j)=y(j-1)+dt*C*sin(t(j-1));
    end
    zci = @(v) find(v(:).*circshift(v(:), [-1 0]) <= 0);                                  
    % Returns Approximate Zero-Crossing Indices Of Argument Vector
    idx_2 = zci(y - 2);                                                                    
% Vector Of Approximate Indices Where ‘y=2’
for k = 1:numel(idx_2)
    t2(k) = interp1(y(idx_2(k)+[-1 1]), t(idx_2(k)+[-1 1]), 2, 'linear','extrap');      
    % Interopolate: ‘t’ Where ‘y=2’
end
 for j=2:N
     t(j)=t(j-1)+dt;
    for k=1:numel(idx_2)
        if t(j)==t2(k)
            C=2;
          y(j)=y(j-1)+dt*C*sin(t(j-1));
        end
    end
 end
plot(t,y)

Thanks again. Now I have realized my error here.

   Final question: How do I write 
        if t(j)==t2(k)+ some tolerance (say 0.5)
      I am trying to select all value of t  which are within 0.5 (or another number) of t2 value.