function c = cntabappend(c,a,b) % non-overflow
%
% c = cntabappend(c,a,b)
%
% Returns vector c plus 1 in the last element, up to the value of b.
% When overflow in the last element, drop it down to  the value of a.
% When i=overflow in all elements, it appends the 1st element to the vector
% c. Its value is a;
% 
% Example:
%  c = 0;
%  for i=1:17
%    c = cntabover(c,1,2) 
%  end
i = length(c);
while i > 0    
    if c(i)+1 <= b
         c(i) = c(i)+1;
         break
    else
        c(i) = a;
        i=i-1;
    end
end
if i == 0 c = [1, c]; end % append new digit