how to take large value i/p

I need to calculate the (a^b)%k(here ^ is not XOR) where (1<=a<=10^1000) and b(1<=b<=10^200) and k is in the long long int range.
But I m not bale to take such long value of a and b.I know k may be used while taking the i/p and modulous arithematic says ((a%k)^(b%k))%k.

So how do we take a and b of such large values

you cannot store such large number in any integer datatype. You have to use strings or character arrays for such huge numbers.

Read here.