Calculating pow(a,b) mod n

Question

I want to calculate a^b mod n for use in RSA decryption. My code (below) returns incorrect answers. What is wrong with it?

unsigned long i         


        

Answer 1

#include 
...
static_cast(std::pow(a,b))%n

but my best bet is you are overflowing int (IE: the number is two large for the int) on the power I had the same problem creating the exact same function.