Summing array elements

What would be the shortest way to sum some elements of an array? For
example from 5 to 50.

I know the "obvious" way to do it:
s=0.
do 1 i=5,50
s=s+a(i)
1 continue

but since I'm currently doing something which requires quite a number
of summing, I was wondering is there something shorter ?

Any idead appreciated

regards
Luka