Pascal program

OK, I just re-red what you are trying to do. So you want to sum the numerical digits in a number.
This means you have to extract the last digit and to add it to a sum number that has the initial value set to 0.

So you do something like this:
n=2013
s=0
s=s+n MOD 10
n=n DIV 10
and you do this until n=0 (2013/10=201;201/10=20;20/10=2;2/10=0 - last digit to add is the first in the number aka 2 and it will always be lower than 10 so your DIV will always be 0) - this is your condition.

If you want to add more numbers and to sum all digits in one huge number, create another var, let's say global_sum=0 and when you finish with the first number ask the user to add another number and then you do global_sum = global_sum+s.
Can't find a Pascal version now but if you want I'll post a C++ version for reference.

In C++ we use "while" statement for this: while(n!=0){instructions_here}

That's what I keep hearing but it's not too practical.
Not saying it isn't but I prefer a more practical approach. I felt more motivated while learning C++ & C#.
But I guess it's just me.

yep learning language which is used only in schools and in some programs remembering late 90'... great idea ;]
it is neither robust, nor programmer friendly... not mentioning those modern and powerful IDEs.

We've been taught pascal when we were on highschool and it was pretty hard to grasp immediately for some.
I remember making a fortune back them coding their assignments. Looking back now I would say python would be the best language to teach for entry level programmers followed by C