C, big numbers and storing them

hi

lets say i had a calculation, and the answer was 128 bit number; and I try and store this into an int, does the overflow occur when the answer was calculated, or does the answer overflow once I attempt to store into an int?

the reason i ask is, I have a way of storing 128 bit numbers (in an array) but I have no idea how I can 'stream' an answer from a calculation (eg bignum * pow(bignum,bignum) into my methods.

what would be helpul if is there is a way of 'streaming' a result from a calculation into an array - is there a way of doing this?

if their isn't I see no alternative but to write my own versions of functions such as pow which handle big numbers

thx