Write a function that determines if a number is prime or not by using Reference

Write a function that determines if a number is prime or not by using Reference

#include 
#include 
int
even (int n)
{
 return (!(n%2));
}

int
prime2 (int n, int *divisor)
{ 
 int i, is_prime;
 
 /* looking for a divisor. if found, it 
  is not a prime number */
 *divisor = 0;

 /* eliminating even numbers except 2 */
 if (even (n))
 {
  if (n==2)
   *divisor=0;
  else
   *divisor=2;
 }
 else
 {
  if (n==1)
   *divisor=0; /* 1 is a prime number */
  else
   /* trying to divide number by 3,5,7,... */
   /* to find a divisor until sqrt(n)      */
   for (i=3; i<=sqrt(n); i=i+2)
   {
    if (!(n%i))
     *divisor=i;
   }
 }
 
 is_prime = *divisor;

 /* if there is a divisor then NOT prime */

 return (!is_prime);
}

int
main (void)
{
int x, div;

   printf ("Enter a positive integer number: ");
   scanf ("%d", &x);

   /*  testing for prime and printing the report */
   if (prime2 (x, &div))
      printf ("%d is a prime number.\n", x);
   else
      printf ("%d not prime number. Divisible by %d.\n", x, div);

return (0);
}