C/C++ :: User Input - Number Prime Or Composite?

User will input a number in the range of 2 and 2^63-1 and the program will decide whether it's prime or not by a simple 'YES' or 'NO'.

I figured out a code:

#include <stdio.h>
#include <string.h>
main() {
unsigned long long n,i=3; int temp=0;
int t;
scanf("%d",&t); //Number of test cases

[Code] ....

Now this code works for normal inputs but whenever I try it with large primes in tat range, like 987654321987654329 or 9223372036854775783 it does not work />.

I tried to print the values of i to check the limit to which it runs.. and I found it 23697, whose square is 561547809 - nowhere near about the input primes.