How compute a cumulative variable through different recursion levels?

Hello all,

I am actually just getting started with recursion and I am struggling with it. I have to solve a problem whose concept is actually very easy, but I don't get right to use the recursion. Without usign loops and any character conversion function, I have to compute the sum of the digits of a number by a recursive function. If the input is 15, the result is 6, if the input is 123, the result is also 6.

This is my code so far:

function result=digit_sum(input)

a=input/10;
b=floor(rem(input,10));

if a<10
    
    result=floor(a)+b; 
else
   %sum here the current value of b for recursion
  result=digit_sum(a);  
end
end

The concept is very easy and funny thing is that the code actually works with 2-digt inputs. With 3 or more digit inputs the could will go through all necessary recursion levels but I don't know how to work with b so that it gets summed with each recursion level.

I assume I need a line of code to sum b afer the else statement, but honestly, I do not know how. If anyone could give a hint I appreciate.

BR,

Carlos.

[Carlos Rueda]

Well, after rethinking this a bit I got the solution, just lurking before my eyes :). I will be happy to tell anyone who is interested and just like me getting started.